LONDON — Second-seeded Victoria Azarenka has pulled out of Wimbledon after hurting her right knee in her opening-round win.

Early in the second set of her match against Maria Joao Koehler, Azarenka did the splits near the baseline, then crumpled to the grass, clutching her right knee and sobbing.

Azarenka recovered after a medical timeout to finish out the 6-1, 6-2 victory on Monday but she moved gingerly after falling and said she wasn't sure about the extent of the injury.

On Wednesday, minutes before her second-round match against Flavia Pennetta was to begin, she pulled out of the match.

Considered one of Serena Williams' toughest matchups, Azarenka has won the last two Australian Opens and had reached the semifinals in her last two Wimbledon appearances.