Venus Williams pulled out of the U.S. Open tournament Wednesday due to Sjögren's Syndrome, an autoimmune disease she had recently been diagnosed with.

I'm really disappointed to have to withdraw from this year's U.S. Open, said the former world number one in a statement. 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.

The two-time champion at Flushing Meadows was set to contest Germany's Sabine Lisicki who reached the semi-finals of Wimbledon tournament this year.

Venus' Career Doomed?

Williams, 31, is recognized as one of the finest players of her generation. The winner of seven Grand Slam single titles has an equally enviable record in doubles and in Olympics. But she has been troubled by serious injuries over the last year. She withdrew from the Australian Open, citing a hip problem, and remained outside the court till this June. Even after her much-awaited comeback, she played only in a handful of matches. After her loss at Wimbledon, she again pulled out of recent tournaments in Toronto and Cincinnati, citing viral infection as the reason.

In this U.S. Open, Williams had an easy victory in her opening match against Vesna Dolonts on Monday which she silenced her critics. But within two days of winning that match and announcing No one is more in one-match-at-a-time mode than me now at this tournament, she went back on her promise.

Now that she is fighting Sjögren's syndrome, an autoimmune disease which causes fatigue and extreme joint pain, her chances of returning to the court are seriously questioned by the experts. Carlos Fleming, Williams' longtime agent, however, believes that she will be better soon and will hit the court with a bang.

What is Sjögren's Syndrome?

Sjögren's syndrome is a chronic disease that reduces moisture production in certain glands. Reports say that more than 1 million Americans have it, and more than 90 percent of them are women.

The most commonly seen symptoms of Sjögren's syndrome are dry eyes and dry mouth, extreme fatigue, acute pain in muscles and joints.

Although the exact cause is unknown, some theories suggest that a virus or bacteria attacks the immune system, causing the white blood cells to destroying exocrine glands that produce tears and saliva. Genetic or inherited factors might also cause the syndrome in some people.

There is no cure, but keeping eyedrops handy and carrying a bottle of water help mitigate symptoms.