Shanghai - Andy Roddick withdrew from the Masters Cup shortly before his match on Wednesday, citing an ankle injury he suffered during training the day before.

The American, who lost his opening match to Andy Murray, will be replaced in the Red group by Radek Stepanek.

The American dropped his bombshell a few hours before he was due to take to the court against Roger Federer.

"I turned it warm up during training, I can't stop and start quickly and don't have much on my serve. It would be a tough prospect to face Roger without a serve."

Roddick, who is playing the season-wrapup event in China for the third straight year, leaves with a 3-5 record at the venue. (dpa)