(EURWEB) Bad knees are running amok among the U.S. Olympic women's team, which just added Serena Williams to the injured roster.

During her semifinal match against 85th-ranked Aleksandra Wozniak, Williams called the trainer while trailing 5-2 in the first set. She got her knee heavily taped by the trainer and came out to finish the set, but appeared to struggle to plant on her injured leg. Wozniak held serve to win the set and won 11 straight points to take a 3-1 lead early in the second.

Williams appeared to injure the knee further while stretching for a backhand in the fifth game of the set and retired. She walked off the court and into the arms of her father, Richard.

Serena's sister Venus and Lindsay Davenport, the other U.S. Olympic singles players, have already pulled out of next week's East West Bank Classic in Carson, Calif., with right knee injuries.