Belarusian Victoria Azarenka, the No. 2 seed, pulled out of Wimbledon Wednesday just minutes prior to her second-round match due to an injured right knee.
Azarenka had been scheduled to take on Italy's Flavia Pennetta in the first match on Centre Court.
The Belarusian, winner of the last two Australian Opens and semifinalist at Wimbledon in 2011 and 2012, defeated Portuguese world No. 106 Maria Joao Koehler 6-1, 6-2 in first-round action on Monday.
Azarenka twisted her knee in a hard fall early in the second set of that match. She required several minutes of on-court medical treatment but managed to finish that contest with her knee bandaged.
She was unable to recover in time, however, to take the court for her match against Pennetta.
Azarenka is the biggest-name injury casualty thus far at Wimbledon.
But four other men's singles players either withdrew prior to their scheduled matches or retired after play had begun on Wednesday due to various ailments: Marin Cilic, Radek Stepanek, John Isner and Steve Darcis, who could not take the court two days after stunning fifth-seeded Rafael Nadal in the first round. EFE