(CNN) -- Venus Williams has announced she is pulling out of the Australian Open due to illness.
The former world number one is suffering from Sjogren's syndrome, an autoimmune disorder which affects energy levels and causes pain in the joints, and missed a large chunk of last season.
Her condition forced the 31-year-old to withdraw from the second round of U.S. Open at the end of August, and restricted Williams to only 11 competitive matches in 2011.
In a statement on her official website the seven-time grand slam champion said: "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.
"I have every intention to return to the circuit in February."
Williams is a five-time Wimbledon champion and twice a winner of the U.S. Open. She was beaten by sister Serena in her only Australian Open final appearance in 2003.
She withdrew from the ASB Classic in New Zealand last week. The Australian Open starts in Melbourne on January 16.