Tennis star Venus Williams withdrew from the last grand slam of the year Wednesday, revealing she is suffering from an autoimmune disease.

The two-time former champion was set to clash with the 22nd seed Sabine Lisicki at the U.S. Open in New York.  Instead Lisicki, who reached the semi-finals of Wimbledon this year, was given a free passage.

The former world number one released her statement talking about her disease, which she had not named until now.

I'm really disappointed to have to withdraw from this year's U.S. Open. I have been recently diagnosed with Sjogren's syndrome, an auto-immune disease which is an ongoing medical condition that affects my energy level and causes fatigue and joint pain. I enjoyed playing my first match here and wish I could continue but right now I am unable to. I am thankful I finally have a diagnosis and am now focused on getting better and returning to the court soon.

Sjogren's is caused when white blood cells, the body's natural defenders against foreign invaders, start attacking the body's moisture-producing glands as well. This often leaves the mouth parched and the eyes scratchy, as if full of sand. The disease also causes joint pain and swelling, according to the Mayo Clinic, reports the Los Angeles Times.

Sjogren's syndrome mostly affects women and most patients develop symptoms after 40. Williams is 31. There is no known cure.

Williams, who won the Wimbledon five times and the U.S. Open twice, has been facing health problems in the past year.

A hip-injury caused her to retire from the Australian Open. She also pulled out of recent tournaments in Toronto and Cincinnati.

Williams won her first round over Vesna Dolonts, but withdrew before the second round match against Lisicki.

I heard she practiced as usual, Lisicki told The New York Times. I saw her in her match clothes so was fully prepared and really looking forward to the match. I hope she will be fine quick.