Defending champion Juan Martin del Potro of Argentina has pulled out of this year's U.S. Open due to a lingering wrist injury.

Del Potro has not played since January 24, when he lost to Croatian Marin Cilic at the Australian Open.

In May, he underwent surgery for a persistent wrist problem and only recently returned to hitting balls.

"I feel extremely sad to announce that I will not to be able to defend my US Open title," the 21-year-old Del Potro said in a statement.

"Winning in New York last year has been my major accomplishment in tennis and my best memory so far. < "I am so sorry for my fans, my sponsors and all the people that care about me, but I have only started practising in the last two weeks and unfortunately I cannot compete at the top level yet."

Del Potro won his first Grand Slam title by rallying to beat five-time U.S. Open champ Roger Federer in five sets in last year's final.