Venus Williams went out of Wimbledon on day one, the first time she hasn't made it through the opening round of the All England tennis tournament since her 1997 debut.
Williams lost 6-1, 6-3 to Elena Vesnina of Russia.
"I did my best today," she told reporters after the match, as quoted by the New York Times. "My opponent played well."
Williams, who has won a total of seven Grand Slams including five Wimbledon titles, was diagnosed last year with Sjogren's Syndrome, a disorder of the immune system which causes fatigue and pain in muscles and joints.
Her health problems forced her to drop out of the 2011 US Open and take six months off – during which time, the BBC said, her world ranking sank to 134th.
She has since made it back up to 58th, but her defeat at the hands of number-79 Vesnina suggests she's nowhere near her previous form.
Williams insists she has no plans to quit, however.
"I have great tennis in me," the Times quoted her as saying. "I just need the opportunity.
"There's no way I'm just going to sit down and give up just because I have a hard time the first five or six freakin' tournaments back."
According to the Associated Press, Williams is still expected to compete in the Wimbledon doubles with her sister, Serena, and in the London Olympics.