Second seed Victoria Azarenka has pulled out of Wimbledon through injury, tournament officials have confirmed.
Azarenka, from Belarus, injured her right knee after a fall in the second set of her first-round victory over Maria Joao Koehler on Monday.
She was due to play first on Centre Court against Italy's Flavia Pennetta on Wednesday, but her withdrawal was confirmed just before the start of the second-round match.
A Wimbledon official said: "Due to injury Victoria Azarenka has been forced to withdraw."
Azarenka slipped in the second set of her 6-1 6-2 first-round win on Court One and let out a huge shriek.
The Belarusian saw out the rest of the match, but she decided that she would not be fit enough to continue in the competition.
Ana Ivanovic's match against Eugenie Bouchard, which was originally due to be played second on Court 12, was switched to be the new opener on Centre Court.