Maria Sharapova is pulling out of the U.S. Open on the eve of the tournament because of a leg injury, the U.S. Tennis Association announced Sunday. It's the second time in three years that the 2006 champion has withdrawn from the year's last Grand Slam event. Sharapova has not played a match since losing to Serena Williams in the Wimbledon semifinals in July. She withdrew from hard-court tournaments in Toronto and Cincinnati in August, citing a right leg strain. Sharapova is a five-time major champion who was seeded No. 2 for the U.S. Open, where play begins Monday. The USTA says Sunday that Daria Kasatkina will replace Sharapova in the main draw.