World number three Maria Sharapova has pulled out of the US Open this month with a shoulder injury.

The four-time Grand Slam champion was seeded third for the tournament, but has now been replaced by Agnieszka Radwanska after inflammation in her right shoulder forced her to withdraw from the competition.

The Russian admits that the decision was a difficult one to make after doing everything she could to try to be fit for Flushing Meadows.

"I have done everything I could since Wimbledon to get myself ready but it just wasn't enough time," Sharapova wrote on her Facebook page. "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.

"It's certainly not an easy decision to make ahead of one of my favourite tournaments, but I know it's the right one that will get me back on the courts soon.

"I plan on taking the next few weeks off, receiving proper treatment and rehabilitation."

Sharapova won the US Open in 2006.