Petkovic was slated to be the 10th seed in the first major tournament of 2012, but persistent back problems forced her to pull out of the event.
Petkovic said after a Tuesday second-round loss to Agnieszka Radwanska at a tournament in Sydney, she decided to have an MRI and a CT scan. The results showed the stress fracture.
"The only thing I can do right now is rest - not walking or sitting a lot - just lying down and hoping that the bone will heal as fast as possible," Petkovic said.
She added that it'll take her six-to-eight weeks to recover from the injury.
"I'm really disappointed because I love Australia," she said. "It's funny, I actually tore my ACL here, but on the other hand I also made my first ever Grand Slam quarterfinal here (2011). So either it's a big high or a big low! I am so sorry that I won't be seeing my fans in Melbourne, because I love the Australians and feel like we have a great connection."
The Aussie Open will get underway next Monday in Melbourne.