BUENOS AIRES, Oct. 14 (Xinhua) -- World No. 4 Juan Martin del Potro faces months on the sidelines after suffering a fractured right knee cap during the Shanghai Masters.
The 30-year-old Argentine was forced to retire during his round-of-16 match against Borna Coric on Thursday after falling during the first set.
"It's a very difficult moment. I feel very sad," Del Potro said in a statement on Sunday. "It's a hard blow that leaves me without strength."
Del Potro has been beset by injuries since winning the 2009 US Open, his only Grand Slam victory to date.
He has undergone four wrist operations over the past decade and at one stage saw his career ranking plummet to 1,045.
The injury looks certain to rule Del Potro out of next month's season-ending ATP World Tour Finals in London.
"Evaluations over the next few days will determine when I can play again. "It's very difficult for me to think about recovery again, I did not expect this to happen," he added.
Serbia's 14-time Grand Slam champion Novak Djokovic won Sunday's final in Shanghai with a 6-3, 6-4 win over Croat Coric.
