Reigning U.S. Open champion Juan Martin del Potro retired from the Shanghai Masters with a wrist injury Wednesday, adding to the mounting injury toll in the event.

The third-seeded Argentine was trailing Austria's Jurgen Melzer 7-5, 2-1 in his second-round match when he retired with an injury to his right wrist.

Del Potro said that he suffered from similar wrist tendinitis earlier in the year at the Miami tournament.

"It's a big tournament here in Shanghai, very important for me," del Potro said. "But if I want to have a good finish this season, I had to recovery, go home to be in good shape for the last tournaments."

Del Potro has already qualified for the eight-man, season-ending ATP World Tour Finals that will take place next month in London.
The Argentine's departure followed that of German Tommy Haas earlier in Wednesday's play.

The 15th-seeded Haas lost the first set 6-4 to qualifier Rainer Schuettler of Germany when he retired with a right shoulder injury.

On Tuesday, fourth-seeded Andy Roddick retired from his match against Stanislas Wawrinka of Switzerland with a left knee injury.

Prior to the tournament starting, world No. 1 Roger Federer withdrew citing fatigue, and Andy Murray pulled out as well with a left wrist injury.

Since winning the U.S. Open last month, del Potro has not shown his best. Last week, he lost to French qualifier Edouard Roger-Vasselin in the first round at the Japan Open in Tokyo.