Petkovic out of Australian Open with back injury

Andrea Petkovic has withdrawn from the Australian Open with a stress fracture in her lower back.

Petkovic, ranked No. 10, lost 7-5, 6-4 to Agnieszka Radwanska of Poland in a second-round match at the Sydney International on Tuesday. She needed an injury timeout during the match to receive treatment from a trainer.

The 24-year-old Petkovic was seeded 10th at the Australian Open, which begins Monday at Melbourne Park.

The German is known for her celebratory dance after she wins - a hip-shaking wiggle that has pleased tennis fans but often irritated her opponents.

She is coming off her best year in 2011, advancing to the quarterfinals of the Australian Open, French Open and U.S. Open and the third round of Wimbledon.