Victoria Azarenka has withdrawn from the Western & Southern Open due to a right knee injury, the tournament announced Tuesday.
Azarenka was the defending champion at the Cincinnati-based event. Rafael Nadal, the defending champion on the men's side, also withdrew with an injury.
Azarenka missed three months in the spring with a left foot injury. She lost in the third round at Wimbledon in June.
Azarenka reached the quarterfinals of last week's Rogers Cup, but lost to Agnieszka Radwańska.
The US Open begins on August 25, after one more tune-up event, the Connecticut Open. Azarenka has lost to Serena Williams in the US Open finals two years in a row.
- Dan Gartland