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The U.S. women’s tennis team, expected to bring glory and gold to its country in the Athens Olympics, has instead brought doctors’ notes.

For the second consecutive day, a projected medalist called in sick.

Wednesday it was Serena Williams, who joined Jennifer Capriati as an Olympic casualty.

Williams was to join her sister, Venus, and other male and female American team members on a flight Tuesday to Athens from Newark, N.J. But she visited Dr. David Altchek in New York during the day and, according to U.S. Olympic Committee spokesman Randy Walker, was told she might aggravate a left-knee injury that has kept her out of recent WTA Tour events.

“I am sad and disappointed, not only because I am unable to travel to Greece and participate in the Olympics but also because I gave my word that I would play,” Williams said in a statement.

So the plane left without her, and her departure reduced the U.S. women’s team of coach Zina Garrison to four players: Venus Williams, Chanda Rubin, Martina Navratilova and Lisa Raymond.

Capriati’s withdrawal because of a hamstring injury resulted in Raymond’s move into the singles draw. But Williams’ withdrawal gave a singles spot to Australian Samantha Stosur.

Raymond got Capriati’s spot because, as a doubles player already entered in the tennis event, she had the next-highest singles ranking for a team without four singles players.

When Williams pulled out, Australia had only three singles players in the draw, and Stosur, at No. 96, ranked higher than the remaining singles possibility for the U.S.–the 47-year-old Navratilova, who has played very few singles events this season.

Venus Williams is the defending champion in both singles and doubles.