Ukraine's Elina Svitolina returns the ball to Germany's Angelique Kerber (not in picture) during their singles match on day 4 of the Women's Tennis Grand Prix WTA 500 tournament in Stuttgart, southwestern Germany, on April 22, 2021. (Photo by Thomas KIENZLE / AFP)

Germany's Angelique Kerber returns the ball to Ukraine's Elina Svitolina (not in picture) during their singles match on day 4 of the Women's Tennis Grand Prix WTA 500 tournament in Stuttgart, southwestern Germany, on April 22, 2021. (Photo by Thomas KIENZLE / AFP)

Germany's Angelique Kerber returns the ball to Ukraine's Elina Svitolina (not in picture) during their singles match on day 4 of the Women's Tennis Grand Prix WTA 500 tournament in Stuttgart, southwestern Germany, on April 22, 2021. (Photo by Thomas KIENZLE / AFP)

Germany's Angelique Kerber returns the ball to Ukraine's Elina Svitolina (not in picture) during their singles match on day 4 of the Women's Tennis Grand Prix WTA 500 tournament in Stuttgart, southwestern Germany, on April 22, 2021. (Photo by Thomas KIENZLE / AFP)

Germany's Angelique Kerber returns the ball to Ukraine's Elina Svitolina (not in picture) during their singles match on day 4 of the Women's Tennis Grand Prix WTA 500 tournament in Stuttgart, southwestern Germany, on April 22, 2021. (Photo by Thomas KIENZLE / AFP)

Germany's Angelique Kerber returns the ball to Ukraine's Elina Svitolina (not in picture) during their singles match on day 4 of the Women's Tennis Grand Prix WTA 500 tournament in Stuttgart, southwestern Germany, on April 22, 2021. (Photo by Thomas KIENZLE / AFP)

Ukraine's Elina Svitolina returns the ball to Germany's Angelique Kerber (not in picture) during their singles match on day 4 of the Women's Tennis Grand Prix WTA 500 tournament in Stuttgart, southwestern Germany, on April 22, 2021. (Photo by Thomas KIENZLE / AFP)

Ukraine's Elina Svitolina returns the ball to Germany's Angelique Kerber (not in picture) during their singles match on day 4 of the Women's Tennis Grand Prix WTA 500 tournament in Stuttgart, southwestern Germany, on April 22, 2021. (Photo by Thomas KIENZLE / AFP)

Germany's Angelique Kerber celebrates winning a rally against Ukraine's Elina Svitolina (not in picture) during their singles match on day 4 of the Women's Tennis Grand Prix WTA 500 tournament in Stuttgart, southwestern Germany, on April 22, 2021. (Photo by Thomas KIENZLE / AFP)

Germany's Angelique Kerber reacts while playing against Ukraine's Elina Svitolina (not in picture) during their singles match on day 4 of the Women's Tennis Grand Prix WTA 500 tournament in Stuttgart, southwestern Germany, on April 22, 2021. (Photo by Thomas KIENZLE / AFP)

Ukraine's Elina Svitolina returns the ball to Germany's Angelique Kerber (not in picture) during their singles match on day 4 of the Women's Tennis Grand Prix WTA 500 tournament in Stuttgart, southwestern Germany, on April 22, 2021. (Photo by Thomas KIENZLE / AFP)

Ukraine's Elina Svitolina returns the ball to Germany's Angelique Kerber (not in picture) during their singles match on day 4 of the Women's Tennis Grand Prix WTA 500 tournament in Stuttgart, southwestern Germany, on April 22, 2021. (Photo by Thomas KIENZLE / AFP)

Germany's Angelique Kerber returns the ball to Ukraine's Elina Svitolina (not in picture) during their singles match on day 4 of the Women's Tennis Grand Prix WTA 500 tournament in Stuttgart, southwestern Germany, on April 22, 2021. (Photo by Thomas KIENZLE / AFP)

Germany's Angelique Kerber returns the ball to Ukraine's Elina Svitolina (not in picture) during their singles match on day 4 of the Women's Tennis Grand Prix WTA 500 tournament in Stuttgart, southwestern Germany, on April 22, 2021. (Photo by Thomas KIENZLE / AFP)

Germany's Angelique Kerber returns the ball to Ukraine's Elina Svitolina (not in picture) during their singles match on day 4 of the Women's Tennis Grand Prix WTA 500 tournament in Stuttgart, southwestern Germany, on April 22, 2021. (Photo by Thomas KIENZLE / AFP)

Ukraine's Elina Svitolina reacts while playing against Germany's Angelique Kerber (not in picture) during their singles match on day 4 of the Women's Tennis Grand Prix WTA 500 tournament in Stuttgart, southwestern Germany, on April 22, 2021. (Photo by Thomas KIENZLE / AFP)

Ukraine's Elina Svitolina returns the ball to Germany's Angelique Kerber (not in picture) during their singles match on day 4 of the Women's Tennis Grand Prix WTA 500 tournament in Stuttgart, southwestern Germany, on April 22, 2021. (Photo by Thomas KIENZLE / AFP)

Germany's Angelique Kerber serves the ball to Ukraine's Elina Svitolina (not in picture) during their singles match on day 4 of the Women's Tennis Grand Prix WTA 500 tournament in Stuttgart, southwestern Germany, on April 22, 2021. (Photo by Thomas KIENZLE / AFP)

Germany's Angelique Kerber serves the ball to Ukraine's Elina Svitolina (not in picture) during their singles match on day 4 of the Women's Tennis Grand Prix WTA 500 tournament in Stuttgart, southwestern Germany, on April 22, 2021. (Photo by Thomas KIENZLE / AFP)

Ukraine's Elina Svitolina (R) is congratulated by Germany's Angelique Kerber (not in picture) after their singles match on day 4 of the Women's Tennis Grand Prix WTA 500 tournament in Stuttgart, southwestern Germany, on April 22, 2021. (Photo by Thomas KIENZLE / AFP)

Ukraine's Elina Svitolina celebrates beating Germany's Angelique Kerber (not in picture) after their singles match on day 4 of the Women's Tennis Grand Prix WTA 500 tournament in Stuttgart, southwestern Germany, on April 22, 2021. (Photo by Thomas KIENZLE / AFP)

Ukraine's Elina Svitolina celebrates beating Germany's Angelique Kerber (not in picture) after their singles match on day 4 of the Women's Tennis Grand Prix WTA 500 tournament in Stuttgart, southwestern Germany, on April 22, 2021. (Photo by Thomas KIENZLE / AFP)

Ukraine's Elina Svitolina returns the ball to Germany's Angelique Kerber (not in picture) during their singles match on day 4 of the Women's Tennis Grand Prix WTA 500 tournament in Stuttgart, southwestern Germany, on April 22, 2021. (Photo by Thomas KIENZLE / AFP)

Ukraine's Elina Svitolina celebrates beating Germany's Angelique Kerber (not in picture) after their singles match on day 4 of the Women's Tennis Grand Prix WTA 500 tournament in Stuttgart, southwestern Germany, on April 22, 2021. (Photo by Thomas KIENZLE / AFP)

22 April 2021, Baden-Wuerttemberg, Stuttgart: Tennis, WTA Tour - Stuttgart, Singles, Women, Round of 16, Svitolina (Ukraine) - Kerber (Germany), Porsche Arena: Angelique Kerber. Photo: Thomas Kienzle/AFP-Pool/dpa

22 April 2021, Baden-Wuerttemberg, Stuttgart: Tennis, WTA Tour - Stuttgart, Singles, Women, Round of 16, Switolina (Ukraine) - Kerber (Germany), Porsche Arena: Jelina Switolina. Photo: Thomas Kienzle/AFP-Pool/dpa

22 April 2021, Baden-Wuerttemberg, Stuttgart: Tennis, WTA Tour - Stuttgart, Singles, Women, Round of 16, Svitolina (Ukraine) - Kerber (Germany), Porsche Arena: Angelique Kerber. Photo: Thomas Kienzle/AFP-Pool/dpa

22 April 2021, Baden-Wuerttemberg, Stuttgart: Tennis, WTA Tour - Stuttgart, Singles, Women, Round of 16, Switolina (Ukraine) - Kerber (Germany), Porsche Arena: Angelique Kerber leaves the court after losing. Photo: Thomas Kienzle/AFP-Pool/dpa

22 April 2021, Baden-Wuerttemberg, Stuttgart: Tennis, WTA Tour - Stuttgart, Singles, Women, Round of 16, Switolina (Ukraine) - Kerber (Germany), Porsche Arena: Angelique Kerber congratulates Jelina Switolina (r) after her victory. Photo: Thomas Kienzle/AFP-Pool/dpa

22 April 2021, Baden-Wuerttemberg, Stuttgart: Tennis, WTA Tour - Stuttgart, Singles, Women, Round of 16, Switolina (Ukraine) - Kerber (Germany), Porsche Arena: Angelique Kerber leaves the court after losing. Photo: Thomas Kienzle/AFP-Pool/dpa

22 April 2021, Baden-Wuerttemberg, Stuttgart: Tennis, WTA Tour - Stuttgart, Singles, Women, Round of 16, Switolina (Ukraine) - Kerber (Germany), Porsche Arena: Jelina Switolina cheers after winning. Photo: Thomas Kienzle/AFP-Pool/dpa

22 April 2021, Baden-Wuerttemberg, Stuttgart: Tennis, WTA Tour - Stuttgart, Singles, Women, Round of 16, Switolina (Ukraine) - Kerber (Germany), Porsche Arena: Jelina Switolina cheers after winning. Photo: Thomas Kienzle/AFP-Pool/dpa

22 April 2021, Baden-Wuerttemberg, Stuttgart: Tennis, WTA Tour - Stuttgart, Singles, Women, Round of 16, Svitolina (Ukraine) - Kerber (Germany), Porsche Arena: Angelique Kerber. Photo: Thomas Kienzle/AFP-Pool/dpa

22 April 2021, Baden-Wuerttemberg, Stuttgart: Tennis, WTA Tour - Stuttgart, Singles, Women, Round of 16, Switolina (Ukraine) - Kerber (Germany), Porsche Arena: Jelina Switolina. Photo: Thomas Kienzle/AFP-Pool/dpa

22 April 2021, Baden-Wuerttemberg, Stuttgart: Tennis, WTA Tour - Stuttgart, Singles, Women, Round of 16, Svitolina (Ukraine) - Kerber (Germany), Porsche Arena: Angelique Kerber. Photo: Thomas Kienzle/AFP-Pool/dpa

22 April 2021, Baden-Wuerttemberg, Stuttgart: Tennis, WTA Tour - Stuttgart, Singles, Women, Round of 16, Switolina (Ukraine) - Kerber (Germany), Porsche Arena: Jelina Switolina. Photo: Thomas Kienzle/AFP-Pool/dpa

22 April 2021, Baden-Wuerttemberg, Stuttgart: Tennis, WTA Tour - Stuttgart, Singles, Women, Round of 16, Svitolina (Ukraine) - Kerber (Germany), Porsche Arena: Angelique Kerber. Photo: Thomas Kienzle/AFP-Pool/dpa

22 April 2021, Baden-Wuerttemberg, Stuttgart: Tennis, WTA Tour - Stuttgart, Singles, Women, Round of 16, Svitolina (Ukraine) - Kerber (Germany), Porsche Arena: Angelique Kerber. Photo: Thomas Kienzle/AFP-Pool/dpa

22 April 2021, Baden-Wuerttemberg, Stuttgart: Tennis, WTA Tour - Stuttgart, Singles, Women, Round of 16, Switolina (Ukraine) - Kerber (Germany), Porsche Arena: Jelina Switolina. Photo: Thomas Kienzle/AFP-Pool/dpa

22 April 2021, Baden-Wuerttemberg, Stuttgart: Tennis, WTA Tour - Stuttgart, Singles, Women, Round of 16, Svitolina (Ukraine) - Kerber (Germany), Porsche Arena: Angelique Kerber. Photo: Thomas Kienzle/AFP-Pool/dpa

round at the 2021 Porsche Tennis Grand Prix WTA 500 tournament against Petra Kvitova of the Czech Republic. 20 Apr 2021 Pictured: April 20, 2021, STUTTGART, GERMANY: Elina Svitolina of the Ukraine talks to the media at the 2021 Porsche Tennis Grand Prix WTA 500 tournament. Photo credit: ZUMAPRESS.com / MEGA TheMegaAgency.com +1 888 505 6342

round at the 2021 Porsche Tennis Grand Prix WTA 500 tournament against Petra Kvitova of the Czech Republic. 20 Apr 2021 Pictured: April 20, 2021, STUTTGART, GERMANY: Elina Svitolina of the Ukraine talks to the media at the 2021 Porsche Tennis Grand Prix WTA 500 tournament. Photo credit: ZUMAPRESS.com / MEGA TheMegaAgency.com +1 888 505 6342

round at the 2021 Porsche Tennis Grand Prix WTA 500 tournament against Petra Kvitova of the Czech Republic. 20 Apr 2021 Pictured: April 20, 2021, STUTTGART, GERMANY: Elina Svitolina of the Ukraine talks to the media at the 2021 Porsche Tennis Grand Prix WTA 500 tournament. Photo credit: ZUMAPRESS.com / MEGA TheMegaAgency.com +1 888 505 6342

round at the 2021 Porsche Tennis Grand Prix WTA 500 tournament against Petra Kvitova of the Czech Republic. 20 Apr 2021 Pictured: April 20, 2021, STUTTGART, GERMANY: Elina Svitolina of the Ukraine talks to the media at the 2021 Porsche Tennis Grand Prix WTA 500 tournament. Photo credit: ZUMAPRESS.com / MEGA TheMegaAgency.com +1 888 505 6342

round at the 2021 Porsche Tennis Grand Prix WTA 500 tournament against Petra Kvitova of the Czech Republic. 20 Apr 2021 Pictured: April 20, 2021, STUTTGART, GERMANY: Elina Svitolina of the Ukraine talks to the media at the 2021 Porsche Tennis Grand Prix WTA 500 tournament. Photo credit: ZUMAPRESS.com / MEGA TheMegaAgency.com +1 888 505 6342

round at the 2021 Porsche Tennis Grand Prix WTA 500 tournament against Petra Kvitova of the Czech Republic. 20 Apr 2021 Pictured: April 20, 2021, STUTTGART, GERMANY: Elina Svitolina of the Ukraine talks to the media at the 2021 Porsche Tennis Grand Prix WTA 500 tournament. Photo credit: ZUMAPRESS.com / MEGA TheMegaAgency.com +1 888 505 6342

round at the 2021 Porsche Tennis Grand Prix WTA 500 tournament against Petra Kvitova of the Czech Republic. 20 Apr 2021 Pictured: April 20, 2021, STUTTGART, GERMANY: Elina Svitolina of the Ukraine talks to the media at the 2021 Porsche Tennis Grand Prix WTA 500 tournament. Photo credit: ZUMAPRESS.com / MEGA TheMegaAgency.com +1 888 505 6342

round at the 2021 Porsche Tennis Grand Prix WTA 500 tournament against Petra Kvitova of the Czech Republic. 20 Apr 2021 Pictured: April 20, 2021, STUTTGART, GERMANY: Elina Svitolina of the Ukraine talks to the media at the 2021 Porsche Tennis Grand Prix WTA 500 tournament. Photo credit: ZUMAPRESS.com / MEGA TheMegaAgency.com +1 888 505 6342

round at the 2021 Porsche Tennis Grand Prix WTA 500 tournament against Petra Kvitova of the Czech Republic. 20 Apr 2021 Pictured: April 20, 2021, STUTTGART, GERMANY: Elina Svitolina of the Ukraine talks to the media at the 2021 Porsche Tennis Grand Prix WTA 500 tournament. Photo credit: ZUMAPRESS.com / MEGA TheMegaAgency.com +1 888 505 6342