MELBOURNE, Australia (AP) — Venus Williams withdrew from the Australian Open on Monday, prolonging her absence from the tennis tour because of an autoimmune disease that can cause fatigue and joint pain.

The seven-time Grand Slam title winner announced on Twitter and her website that she wouldn’t play in the year’s first major tournament, which starts next week. She added, 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.

“I regret to announce that I am withdrawing from the 2012 Australian Open. After several months of training and treatment, I am making steady progress to top competitive form. My diet and fitness regimen have allowed me to make great strides in terms of my health and I am very close to being ready to return to WTA competition,” Williams said in a posting on her website Monday. “I have every intention to return to the circuit in February.”

Australian Open tournament director Craig Tiley said Williams was “very disappointed” that she was not able to play in Melbourne.

“She had hoped she’d be further along in her preparation but is not quite ready for Grand Slam competition,” Tiley said in an email to The Associated Press. “She’s an amazing champion and she’s had a tough year battling illness and injury. We wish her all the best and look forward to seeing her back in Australia soon.”

Top-ranked Caroline Wozniacki, a former doubles partner of Williams, said the American’s health must come first.

“She’s been unlucky with the virus thing,” Wozniacki said after her second-round win Tuesday at the Sydney International. “I’m not completely sure what it is exactly, but the most important thing is the health.

“Tennis, it’s a game. I’m sure she’ll come back and fight and try to come back to the top again. But most of all, the most important thing is that you’re healthy. Hopefully she’ll be 100 percent healthy by February.”