Defending champion Victoria Azarenka has withdrawn from the Western & Southern Open because of a right knee injury.
The WTA says Azarenka withdrew after practicing on Tuesday. Azarenka was replaced in the draw by Mona Barthel.
Azarenka injured her knee in her first-round win at Wimbledon and played in two tournaments after the grass-court major.
She hopes to be ready for the U.S. Open, which starts Aug. 25.