Sam Stosur has withdrawn from her quarterfinal against Angelique Kerber at the BNP Paribas Open because of a right calf injury.
Kerber will move into the semifinals against either top-seeded Victoria Azarenka or No. 8 Caroline Wozniacki, who play later on Thursday.
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.