INDIAN WELLS, Calif. -- Defending champion Victoria Azarenka has withdrawn from the BNP Paribas Open because of a right ankle injury that had been bothering the world's second-ranked player since before the tournament began.
Azarenka had been scheduled to play No. 8 seed Caroline Wozniacki in a quarterfinal match Thursday afternoon that would have pitted two former top-ranked players against each other.
Azarenka says she was in too much pain while warming up to try to play. She says a doctor advised her to rest because her ankle has inflammation and tendinitis in it.
She was the second player to withdraw on Thursday. Earlier, No. 7 seed Sam Stosur pulled out of her quarterfinal against Angelique Kerber because of a right calf injury.
Kerber and Wozniacki will move into a semifinal against each other.
Stosur says she hurt her calf muscle in the last game of a three-set win against Mona Barthel on Tuesday. The Australian didn't practice on Wednesday and iced her leg. Stosur was five minutes into her warm-up on Thursday when she realized she couldn't play.
She says this is only the second time she's pulled out of a match in her career and isn't sure how long she'll be sidelined.