Venus Williams autoimmune disease

New York: Former U.S. Open champion Venus Williams withdrew from the last grand slam of the year on Wednesday after revealing she is suffering from an autoimmune disease.

The former world number one quit the tournament before her second round match against Germany's Sabine Lisicki and then released a statement explaining her health problems.

"I'm really disappointed to have to withdraw from this year's U.S. Open," she said in the statement. "I have recently been diagnosed with Sjogren's Syndrome, an autoimmune disease which is an ongoing medical condition that affects my energy level and causes fatigue and joint pain."Williams, who has been battling health problems for the past year, retired from her third round match at the Australian Open with a hip problem and did not play again until June.

The 31-year-old played only a handful of matches because of what she said was an "energy-sucking" mystery illness.

She won her first round clash with Vesna Dolonts of Russia 6-4 6-3 on Monday even though there were signs she was below her best.

"I enjoyed playing my first match here and wish I could continue but right now I am unable to," said Williams. "I am thankful I finally have a diagnosis and am now focused on getting better and returning to the court soon."

Williams has not won a grand slam singles title since 2008.

Speculation about her future has intensified over the past few months but earlier this week she confirmed she had no intentions of retiring.