New York City: The U.S. Tennis Association announced the withdrawal of the 2006 champion, who has played only one match on tour since her second-round loss at Wimbledon in June.
Sharapova originally was seeded third at the U.S. Open. The USTA said 2012 Wimbledon runner-up Agnieszka Radwanksa would shift from No. 4 to No. 3, and all other seeded players below her would move up a spot, too.
"I just wanted to let you know that withdrawing from the U.S. Open has been a really tough decision to make. I have done everything I could since Wimbledon to get myself ready but it just wasn't enough time," read a message posted on Sharapova's Facebook page on Wednesday. "I have done many tests, received several opinions and it all comes down to taking the proper amount of time to heal my shoulder injury properly."