Andy Roddick was also forced to retire in his second-round tie, and the news of del Potro’s withdrawal will only add fuel to the fire burning over the length of the gruelling ATP schedule.
Del Potro was a set down to Melzer when he was forced to pull out with a wrist problem. The US Open champion has already secured his place at next month’s ATP World Tour Finals in London.
Del Potro and Roddick add themselves to the already lengthy injury list including Roger Federer (fatigue) and Andy Murray (wrist).
Meanwhile Rafael Nadal marched through to the third round of the event in Shanghai after a three-set thriller against USA’s James Blake, setting up a tie with Tommy Robredo.
Novak Djokovic will play Rainer Schuettler after the Serb disposed of Italian qualifier Fabio Fognini in the second round.
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BIOGRAPHY: Marcus Rashford