Venus Williams has pulled out of the U.S. Open. Williams was scheduled to play German Sabine Lisicki in the third match on Arthur Ashe Stadium on Wednesday, but pulled out while the second match on Ashe, between Andy Murray and Somdev Devvarman, was taking place.

"I'm really disappointed to have to withdraw from this year's U.S. Open," Williams said in a statement on her withdrawal. "I have been recently diagnosed with Sjögren's Syndrome, an autoimmune 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."

Venus' agent, Carlos Fleming, told TENNIS.com that he and the rest of her camp were all ready to go on court to watch her play Lisicki. "I really don't know what's going on. Clearly I'm very worried," he said. "We were all excited about her playing here."

Venus walked out of the facility smiling but with her head down around 4:40 PM.

Venus hadn’t played a match since Wimbledon and had barely been able to practice since that time due to a hip injury and mysterious virus. She still managed to pull off a 6-4, 6-3 victory over the Russia's Vesna Dolonts in the first round, but the injury-riddled 31-year-old later said it took all she could muster just to get on court, and that she had only been practicing for a week. Williams said that the virus, which took her out of the tournaments at Toronto and Cincinnati, had been sucking the energy out of her. She has only played five tournaments since last year's Wimbledon and was forced retire against Andrea Petkovic at the 2011 Australian Open with a hip injury, the first time she's retired at a major in her 17-year career.

"A lot of the battle is just trying to be fit and stay healthy," she after the Dolonts match. "Sometimes I've been losing that battle a lot...I'm never down. I started to get down this summer because all these things are out of my control. It's easier if it's something I've done, that I can control.  When it's out of your control, at some point it does start to be frustrating."