WASHINGTON (AP):

Defending champion Juan Martin del Potro withdrew from the United States Open yesterday saying he "cannot compete at the top level yet" after having an operation on his right wrist in May.

He becomes only the third US Open men's champion in the 42-year Open era who didn't defend the title. And del Potro's announcement arrives a day after Serena Williams became the first No. 1 in the 35-year history of the women's rankings to miss the US Open. She still is recovering from surgery for cuts on her right foot.

Del Potro has not played on tour since the Australian Open in January because of an injury to his right, racket-swinging wrist.