Credit: EMMANUEL DUNAND/AFP/Getty Images

Venus Williams will be watching the rest of the U.S. Open from the sidelines.

The 31-year-old tennis player pulled out of the tournament Wednesday, citing medical reasons. Williams was recently diagnosed with Sjogren's syndrome, an autoimmune disease that causes fatigue and joint pain.

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

Williams' withdrawal allowed tennis pro Sabine Lisicki to move forward to the third round. "I think she's a tough girl and I think she'll come back," Lisicki said of Williams. "You know, it would be unfortunate if she couldn't."