Victoria Azarenka's bid to become the first woman in more than 20 years to successfully defend her Indian Wells title crashed to a halt Thursday as she pulled out with an injury.
The world No. 2 from Belarus pulled out shortly before her scheduled quarter-final clash with eighth-seeded Caroline Wozniacki, granting the Dane a semi-final berth on a walkover.
In an odd twist, Wozniacki's semi-final opponent also advanced on a walkover on Thursday as fourth seed Angelique Kerber went through when Samantha Stosur pulled out with a calf injury.
Organizers announced that Azarenka had a right ankle injury, and the Australian Open champion had spoken of ankle pain after her 6-3, 6-1 fourth-round victory over Urszula Radwanska.
But she said an MRI performed Wednesday showed inflammation and tendinitis in her foot, and doctors had told her rest was the best medicine.
"There is big inflammation and tendinitis," she said. "It cannot get better with me playing on it, especially playing last three matches on it, it's just worse.
"I tried not to practice yesterday and see if it will settle down a little bit.
"I felt yesterday was better, not walking in my tennis shoes. But today, once I started doing the exercise, that was it."
Azarenka said she still hoped to play the elite hard-court tournament starting in Miami next week.
She planned to travel to Florida on Sunday, but would have to see how the injury responds to rest and treatment.
"That's frustrating for me as a player, not knowing," she said over the uncertainty of her expected recovery time. "Sometimes you think, OK, well, I rest three days and I'm going to be fine with it.
"But when you don't know the healing process it's a little bit frustrating. I'm going to give my 200 percent to do everything I can for treatment and just be focused on that. That's going to be my priority to get ready (for Miami)."
Azarenka is unbeaten on the court in 2013, a 17-0 run that includes the Australian Open and a title in Doha.
But this is the second time she has surrendered a walkover. She withdrew before her scheduled semi-final against Serena Williams in Brisbane with an infected right toe that resulted from a pedicure.
Azarenka, who routed Maria Sharapova in last year's final, was trying to become the first woman since Martina Navratilova in 1990-91 to win back-to-back Indian Wells titles.
"I tried absolutely everything I could to do, but I have been advised by the doctor, by my own team, that it's just a very high risk to make it much worse," she said of her decision to withdraw.