Andrea PetkovicWith the 2012 Australian Open just around the corner, the tournament withdrawals are mounting. Today, the No. 10 seed, Andrea Petkovic of Germany withdrew with a stress fracture in her lower back. The injury could keep her sidelined for two months.

Petkovic 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 time-out during the match to receive treatment from a trainer.

Earlier in the week, Venus Williams of the USA withdrew, prolonging her absence from the tennis tour because of an autoimmune disease that can cause fatigue and joint pain. Venus, a seven-time Grand Slam champion announced on her website that she wouldn’t play in the year’s first major tournament, adding though that she plans to be back in action next month.

Williams hasn’t played competitively since Aug. 29 at the U.S. Open. Two days later, she pulled out of that tournament, revealing that she’d been diagnosed with Sjogren’s syndrome. The layoff has dropped the former No. 1 to 100th in this week’s WTA rankings.

Kim Clijsters of Belgium is also in doubt. Clijsters quit the Brisbane event with a hip flexor injury putting her Australian Open title defense in serious danger.

Maria Sharapova of Russia also did not start in Brisbane due to an ankle worry, but has been practicing in Melbourne in recent days. And Serena Williams of the USA was unable to play at Brisbane after injuring her ankle.

So stay tuned, folks. It is shaping up to be an interesting start to the year on the WTA tour.