Seven-time Grand Slam singles champion Venus Williams withdrew from the Australian Open as she struggles to return from the autoimmune disease Sjogren's syndrome. In a posting on her website, the US star said that she has been making progress and plans to return to WTA Tour play in February, when events begin in the United States. "I regret to announce that I am withdrawing from the 2012 Australian Open," Williams said on her website. "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. I have every intention to return to the circuit in February." Williams, whose ranking has slipped to 100th in the world, pulled out of last week's WTA event in Auckland because of the illness, which saps her energy and causes pain in her joints. World number one Caroline Wozniacki said Williams's health was the most important thing. "Venus has played for many years, but she's been unlucky with the virus thing," Wozniacki said at the Sydney International. "I'm not completely sure what it is exactly, but the most important thing is the health. Tennis is a game but most of all, the most important thing is that you're healthy and she'll be 100 percent healthy by February." Williams, 31, is not the only member of her family in doubt for the first Grand Slam event of 2012. Younger sister Serena, a 13-time Grand Slam singles champion, pulled out of last week's event at Brisbane with a sprained ankle. Serena Williams posted a Twitter message saying she was doing better, hinting she might be ready for the Melbourne fortnight that begins on Monday.