Wimbledon champion Garbine Muguruza was one of three players forced to retire in the last 16 of the Stuttgart Open due to leg injury.
Germany's Angelique Kerber sustained leg injury going down against Estonia’s Anett Kontaveit and withdrew.
Czech Marketa Vondrousova also quit with a leg problem after winning first set against Ukraine’s Elina Svitolina.
Third seed Svitolina, who recovered to lead 2-6 6-1 3-2 before Vondrousova's retirement, will now play French sixth seed Caroline Garcia, who overcame Marta Kostyuk of Ukraine 6-1 3-6 7-5.