Andrea Petkovic sprains ankle, retires to Victoria Azarenka

Andrea Petkovic retired trailing No. 1 Victoria Azarenka 2-6, 4-4 on Thursday after injuring her right ankle during the second round of the Porsche Grand Prix in Stuttgart, Germany. She was helped off the court by Azarenka, who was visibly shaken up by the incident during her postmatch interview. Petkovic, who said she'll get an MRI and scans on Friday, was reportedly seen leaving the site in a wheelchair.

That's some horrible luck for Petkovic, who's been snakebit by injury throughout her career. A torn ACL ruled her out of most of 2008, and she needed surgery to repair her right knee last year after suffering a meniscus tear in Cincinnati. Now, in just her third match back from a three-and-a-half-month layoff to heal a stress fracture in her back, she goes down with what looks like a bad ankle sprain.

Here's video of the injury as it happened, which is not for the faint of heart. And kudos to Azarenka for her sportsmanship throughout the incident, running off to get Petkovic some ice and then helping her off the court. Nice to see.

(Note: The video shows a painful-looking injury in slow motion. Watch at your own discretion.)