NEW YORK (AP) -- Venus Williams says she "absolutely" plans to return to tennis after she withdrew from the U.S. Open because of a recently diagnosed autoimmune disease.
Williams revealed Wednesday after pulling out of her second-round match that she had Sjogren's syndrome, which can cause fatigue and joint pain.
"I think the best thing that could have happened for me this summer was to feel worse so I could feel better," Williams said in an interview Thursday with ABC's "Good Morning America."
The seven-time Grand Slam champion said she'd had problems with stamina for several years, which she now believes were caused by Sjogren's. It wasn't until she developed more concrete symptoms in the last few months that she was diagnosed.
"Sjogren's is something you live with your whole life," Williams said. "The good news for me is now I know what's happening after spending years not knowing. ... I feel like I can get better and move on."
She said she suffered from swelling, numbness and "debilitating" fatigue.
"It's not that you don't have energy; you just feel beat up," the 31-year-old American said.
Williams said she initially thought of playing at the Open.
"OK, I could walk out on the court. I'm a tough woman. I'm a tough athlete. I've played through a lot of things," she said. "But what kind of match it would be? It was a tough decision, but at the same time I've had to come to accept what I'm going through."
Williams had cited a virus in withdrawing from hard-court tuneup tournaments after losing in the fourth round at Wimbledon in late June. She played for the first time in two months Monday, beating Vesna Dolonts 6-4, 6-3 in the first round in New York.
According to the Sjogren's Syndrome Foundation website, the disease is a chronic autoimmune illness in which white blood cells attack moisture-producing glands. Common symptoms include dry eyes and dry mouth. As many as 4 million Americans have the disease.
Despite all of her past success, including a brief stint at No. 1, Williams was unseeded at the U.S. Open. She's fallen to 36th in the rankings after a year of little action. Since reaching the semifinals at the 2010 U.S. Open, Williams has played only 11 matches. The WTA projects her ranking now will slide out of the top 100.
It's been a year of health scares for the Williams sisters. Younger sister Serena suffered from a blot clot in her lungs over the winter. Serena Williams plays in the second round of the U.S. Open on Thursday.
Venus said Serena's travails had already given her a new perspective.
"So this, right now, I think will help me to feel grateful for everything that I have," she said. "And at the same time it makes me want to get up and fight harder every single day."