NEW YORK - There is always skepticism about the Williams sisters, some of it unjustified, some of it very logical.

The questionable injuries, such as when Venus pulled out four minutes before a scheduled semifinal against Serena at Indian Wells because of tendinitis.

The often expressed belief, especially among other players, when in the early years Serena and Venus faced each other, the winner was predetermined, by their father, Richard.

The implied impression that at times they would rather be acting or designing clothing, doing anything rather than reaching the summit of the tennis world, where they had been through the years.

So when the announcement was made in the media room Wednesday, less than an hour before her much anticipated second-round U.S. Open tennis match against Sabine Lisicki, that Venus had withdrawn because of an "unspecified illness,'' the comments were less than sympathetic.

More like, "Sure. What is it this time?'' This time it turns out to be something serious and debilitating. This time it could be an ailment which puts a stop to one of the game's great careers, a career with Venus at 31 already in decline.

Venus has been stricken with one of those diseases with a name as frightening as the disorder, "Sjogren's Syndrome, an autoimmune disease, which causes joint pain and affects energy level.

According to a Mayo Clinic definition, the syndrome is identified by dry eyes and dry mouth  ... often accompanies other immune-system disorders such as rheumatoid arthritis and lupus  ... although you can develop Sjogren's at any age, most people are older than 40 at time of diagnosis. The condition is much more common in women.''

Venus Williams, winner of seven Grand Slam singles titles (Serena has 13) has a long way to go before 40. But how much longer does she have to go in her career?

Treatment can relieve the symptoms, but Venus, who tried to keep the identity of the disease a secret after her opening-match win Monday night, concedes her energy level is down and she is fatigued.

"I'm really disappointed to have to withdraw from this year's U.S. Open,'' Venus said in a statement.

Deep down, she may be more frightened than disappointed. Fatigue and joint pain are worrisome propositions for any athlete, particularly a tennis player whose game has been constructed on power and speed.

A year ago the golfer Phil Mickelson, a decade older than Venus, was diagnosed with psoriatic arthritis, which affected his joints, causing a great deal of pain and creating doubt among others whether he would be forced to retire. But using designated drugs and changing his diet, Mickelson has continued to play, finishing tied for second in the recent British Open.

Tennis, certainly, is different from golf, but there are drugs to battle Sjogren's syndrome. And Venus, through the statement, indicated she hoped to go on playing.

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

Venus had played only three tournaments during the year prior to defeating Russia's Vesna Volants, 6-4, 6-3, Monday night on Arthur Ashe Court, none since losing in the fourth round at Wimbledon at the end of June.

She had withdrawn from tournaments in April and May because of hip and abdominal injuries, then after consecutive starts in June at Eastbourne and Wimbledon, again was unable to play because of what was listed as viral illness.

Now she and we know the identity of that illness. What nobody knows is how long it will take her to recover and make yet another comeback.

To her credit, despite the numerous illnesses and injuries, when Venus went out to play there were no excuses. Two years ago after a loss at Wimbledon, a British journalist asked Venus sympathetically, "Are you hurt?''

Venus responded emphatically. "If you play, you're not hurt,'' she said. "If you're hurt, don't play.''

She's not hurt specifically. Rather she's hurting, in pain. So is tennis in America, which, still searching hopelessly for replacements, needs Venus and Serena, the only women players from the U.S. who have won Slams and whose appearances or disappearances get noticed.

It has been a difficult period for the sisters, Serena, after her victory at Wimbledon in 2010, missed the next 11 months of competition after two operations to repair a torn tendon in her right foot and then was hospitalized to recover from blood clots in both lungs and a hematoma that required more surgery.

Now Venus discloses she has a disease alien to most of us.

Serena's back, and once more among the best in the game. Whether that ever will be said again about Venus no one dare predict.