Roger Federer hopeful of Shanghai start

Roger Federer is hopeful of beginning his defence of the Tennis Masters Cup despite struggling with a back injury.

The world number two pulled out of last week's Paris Masters and is taking painkillers in order to be ready for his first match on Monday.

"I haven't been pushing it to the very limits," Federer said. "But so far I've been serving without pain, I've been playing without pain."

The end-of-season tournament is already without world number one Rafael Nadal.

And there are doubts about Argentina's Juan Martin del Potro, who is being hampered by a painful right toe.

The loss of Federer, who is now the top seed, would seriously weaken the field after Nadal cited fatigue as a reason to skip the Chinese event, with the Davis Cup final due to begin on 21 November.

The Spaniard also pulled out of last week's event in France, but although Federer said his condition had improved since then, he was still cautious.

"Maybe if I push too early in practice then I'm back to where I was last Thursday and then things are not looking good at all," the Swiss added.

"I think this problem I have with my back needs as much time as possible. Hopefully I'm just going to get ready for Monday and then things are going to be fine."

Del Potro has been bothered by a split big toenail since the US Open and was forced to pull out of last month's Vienna Open, beating only one top-10 player since.

The Argentine opens the tournament on Sunday against world number three Novak Djokovic, with France's Jo-Wilfried Tsonga facing Nikolay Davydenko in the later match.

On Monday, Federer plays against Gilles Simon of France while Britain's Andy Murray will begin his campaign against American Andy Roddick.

Federer is looking to win his fifth end-of-year title and his third on the trot.