Shanghai, China -- (Sports Network) - American Andy Roddick withdrew from the Tennis Masters Cup on Wednesday because of an ankle injury.

Roddick, who lost his first round-robin match on Monday to Andy Murray, was hurt while practicing Tuesday.

"When I was doing a warm-up drill in practice I just went over on it," said Roddick. "We tried as much as we could to get it better."

Roddick was set to face Roger Federer on Wednesday in round-robin action at the season-ending event. He was replaced in the draw by Radek Stepanek of the Czech Republic.