Shanghai - World number one tennis player Rafael Nadal is suffering from serious physical problems, the president of the International Tennis Federation (ITF), Francesco Ricci Bitti, said on Wednesday.

"Nadal has a very serious problem," Ricci Bitti told a small group of media, including Deutsche Presse-Agentur dpa, at the Masters Cup tournament in Shanghai.

Shanghai - Andy Roddick withdrew from the Masters Cup shortly before his match on Wednesday, citing a right 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 Czech Radek Stepanek.

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

"In practise I just went over on it, we tried as much as we could to get it better," he said. "I can't really stop and start very quickly. It's anything when I go kind of over on the outside it hurts.

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.

Shanghai - Andy Roddick withdrew form the Masters Cup shortly before his match on Wednesday, with his place taken by Radek Stepanek.

Shanghai  - Novak Djokovic couldn't be more pleased after reversing his 2007 run of year-end bad luck by qualifying a year later for the semi-finals of the Masters Cup.

The world number three Serb, who cemented his place with a three-set victory Tuesday over Nikolay Davydenko, goes into his last red group match against Jo-Wilfried Tsonga relaxed and calm.

Shanghai - Juan Del Potro didn't allow his mind to stray to the upcoming Davis Cup final as he handed Frenchman Jo-Wilfried Tsonga a 7-6 (7-4), 7-6 (7-5) Gold group defeat at the Masters Cup on Tuesday.

The clash between the pair of 2008 breakthrough rookies at the season-ending championships gave the Argentine a 1-1 record and saddled Australian Open finalist Tsonga from France with two defeats from as many matches.

"I'm in the Masters Cup, I want to be alive until the finals, if I can," Del Potro said.