Del Potro pulls out of U.S. Open title defense

"Winning in New York last year has been my major accomplishment in tennis and my best memory so far."

The tournament starts on August 30 and has already lost the women's world number one Serena Williams who pulled out on Friday with a foot injury.

Del Potro played in the Australian Open but pulled out of a series of tournaments after that and announced in May he was having surgery and would almost certainly miss the three remaining grand slams.