Indian Wells - Australia's Samantha Stosur was forced to withdraw from her Indian Wells quarter-final match against Angelique Kerber due to a right calf injury on Thursday.
Former US Open champion Stosur was seeded seventh and held a 2-0 career record over fourth-seeded German Kerber, who receives a walkover into the semi-finals where she'll face either world number one Victoria Azarenka or Caroline Wozniacki.
"I hurt my right calf muscle in the last game of my match against Mona Barthel when I was serving for the match, so I don't know if you can get any more unlucky than that," said Stosur.
"I think we only played another four points in that match. I felt something go in my calf and it was hurting a fair bit. Yesterday I took the day off practice and only did treatment, probably iced it about 10 times.
"This morning I thought I would give it a shot, and tried to go out and warm up, and after about five minutes I knew that there was no chance I could play, unfortunately."
The injury has also put a cloud over her participation in the Miami WTA event which takes place later in the month.
"I'll talk to the physios and the doctors and work out a good plan for how many days off I need to take off and go from there," said Stosur.
"It's all a bit up in the air at the moment because I've never been through this type of injury before, so it's a matter of wait and see, talking to the people who know and reassessing each day."
Results on Thursday from the ninth day of the ATP Masters and WTA BNP Paribas Open (x denotes seeded player):
Tomas Berdych (CZE x6) bt Kevin Anderson (RSA) 6-4, 6-4
Rafael Nadal (ESP x5) bt Roger Federer (SUI x2) 6-4, 6-2
Angelique Kerber (GER x4) bt Samantha Stosur (AUS x7) - walkover
Caroline Wozniacki (DEN x8) bt Victoria Azarenka (BLR x1) - walkover