Maria Sharapova of Russia fields questions from the media after withdrawing from the tournament due to injury after her loss to Na Li of China during round robin play of the TEB BMP Paribas WTA Championships Istanbul at the Sinan Erdem Dome on October 26, 2011 in Istanbul, Turkey.

Maria Sharapova pulled out of the WTA Championships with a sore ankle Wednesday after losing her second straight match at the season-ending tournament.

Her decision ensured that Denmark's Caroline Wozniacki would become year-end world number one for the second successive year.

Sharapova injured her ankle in Tokyo recently and only just recovered in time to compete in Istanbul. However, after losing 7-6 (4), 6-4 to Li Na in her second round-robin match Wednesday, Sharapova said "the ankle didn't recover as well as I had hoped after the first round."

"The swelling got a little worse," the second-ranked Russian said. "It just limits my movement a lot, and it's not something I really want to risk, especially at the end of the season, knowing that I have some time to recover and let it heal naturally instead of really pushing it and damaging something else."

The Russian will be replaced by alternate Marion Bartoli of France, who will face Victoria Azarenka of Belarus in the final group round.