WIMBLEDON, England -- Defending champions Venus and Serena Williams pulled out of the women's doubles at Wimbledon on Tuesday after Serena, beaten in the singles quarterfinal by Jennifer Capriati, said she had been sick for four days.

Curry Kirkpatrick's Take

Kirkpatrick As Jennifer Capriati defeated Serena Williams, 6-7 (4-7), 7-5, 6-3, for the fourth time in a row, it was sometimes difficult to believe that the former was winging toward the third leg of the Grand Slam, the latter was the Big W insiders' pick to stop her and win the tournament herself and that both were among the best players in the world -- rather than a couple of shrieking, bumbling, gagging, physically depleted characters in need of a M*A*S*H* clinic. Or a psychiatrist's couch. Complete Kirkpatrick column

The sisters had been scheduled to meet Martina Navratilova and Arantxa Sanchez-Vicario on Centre Court but reported to the referee's office that Serena's stomach sickness would keep them from playing.

"For four days now I've just been struggling," said Serena, who needed to leave Centre Court to use the bathroom when she was 4-0 down in the third set to Capriati.

"I was really nauseated," Serena Williams said. "I just had to get out of there. I don't know how I came back.

Capriati was surprised by the interruption.

"I had no idea until she took the bathroom break," Capriati said. "I just asked the umpire. ... It was an emergency. I didn't want to know the details."

"(Friday) was when I got this sickness. I haven't been able to really eat since. I haven't been right since. I went to the doctor twice, it was a viral infection. I think maybe I've had it for a while and it's just come to its apex now," Serena said.

Williams, seeded fifth, lost 6-7 (4), 7-5, 6-3 to the fourth-seeded Capriati.

She said she had considered pulling out of the singles tournament in an earlier round against Magdalena Maleeva.

"I went to the WTA (Women's Tennis Association) and it was like 'I don't know if I can do it.' I don't know how I got through. I was thinking about pulling out before that match," Williams said.

The WTA said Serena on Saturday had gastroenteritis, an upset stomach due to virus. She withdrew from doubles after being checked by a doctor and trainer following her singles loss.

WTA trainer Michelle Gebrian checked Serena Williams and Capriati on the court. She said she gave Williams medicine to settle her stomach.

"I think Serena was deteriorating throughout the match," she said.

"I just have no energy," Serena Williams said. Usually I'm such a strong person, I'm very well conditioned. It's just like I'm just totally going on emotion, not anything physical at all."