MIAMI -- Juan Martin del Potro, the 2009 US Open champion, planned to have an operation on his right knee Monday, according to a statement from his team posted on Instagram.

The statement said the 31-year-old Argentine had surgery in June but needs another procedure because of pain that wouldn't let him run or jump and made walking up stairs difficult.

Del Potro fractured his right kneecap for the second time in less than a year while playing last year at a grass-court tournament to prepare for Wimbledon. He hasn't competed since.

Del Potro ended Roger Federer's 40-match US Open winning streak by beating him in five sets in the final at Flushing Meadows 11 years ago. Del Potro has dealt with a long series of injuries since then, mostly to his wrist and knee.

His career-best ranking was No. 3, and he is currently No. 121 after his long absence from the tour.