Injured Roddick pulls out of Masters Cup

SHANGHAI (Reuters) - World number six Andy Roddick pulled out of the $4.45-million Masters Cup on Wednesday because of a right ankle injury.

The 26-year-old American lost his opening match in the season-ending championship for the world's top eight players to Andy Murray on Monday and had been due to play top seed Roger Federer in his second group encounter later on Wednesday.

"It was during a warm-up drill in practice yesterday, I just went over on it," the former world number one told reporters.

"I can't really stop and start very quickly. It's definitely a tough prospect trying to beat Roger with no serve and not being able to move much."

First alternate Radek Stepanek, the Czech world number 27, stepped in to take on Federer in the round-robin stage, losing a tight match 7-6 6-4.

Roddick, who was playing in his fifth Masters Cup, said the injury should not disable him for too long.

"They don't think it's too long term, which is nice," he said. "It's unfortunate for this event as far as I go but I don't think we're looking at anything more than a week or so.

"I'm very much looking forward to getting healthy and actually having some time to try to get fit again and be prepared going forward next year."

The 2003 U.S. Open champion emphasized that his injury was the result of an accident but did not pull his punches when asked about the danger of the top men playing too much tennis.

"I think too much is asked of us as far as playing 11 months of the year and now they're imposing more mandatory tournaments," he said.

"It doesn't make a whole lot of sense...at a certain point you would hope they start respecting our opinions a little bit more."

Despite the late call-up, Stepanek felt he had acquitted himself pretty well against Federer, whom he beat at the Rome Masters in May.

"I think I played a very good match today against Roger, which was very tight." he said. "You know, it was a question of a couple of points."

The Czech will earn at least $70,000 for playing two matches at the Qizhong arena and even if his loss to Federer means he cannot now reach the knockout stage, he said he would do his best to beat Frenchman Gilles Simon on Friday.

"You know, for me it's honor to be here," he said. "I'm enjoying my time a lot here.

"The chance came today to compete here. You know, for me it was always a dream to play in the Masters Cup because you're in the elite eight best players in the world."

(Editing by Clare Fallon)