Federer feels no pressure as he defends ATP title at The O2

Federer, who has slipped to four in the world rankings, won last year with a convincing demolition of Rafael Nadal in the final. He said the pressure doesn't affect him.

He said:"Not really. I've done it so many times the pressure's more just having to face a Top Ten guy in the first match, that's where I find the pressure lies for me.

"Here I am entering again as defending champion and I hope I have a chance to do well and finish the year strong.

"It would be amazing to win the sixth time. I've had so many successful ends to the years and this is another one with wins in Basel and Paris."

As well as Federer and Nadal, Novak Djokovic and Andy Murray are strongly fancied to lift the trophy a week on Sunday, and the 30-year-old Swiss said not to rule out the lower ranked players Mardy Fish, Jo-Wilfried Tsonga, David Ferrer and Tomas Berdych.

He said: "This year it's very interesting because the one to four guys are the favourites bit the five to eight guys have the potential to upset the top guys and even go all the way.

"Tsonga and Fish, Ferrer and Berdych all have big games that can be extremely dangerous on any given day. They are good enough to win this.

"The top four guys are in good shape. Novak's arm should be okay after his arm [injury} and Rafa might be a touch rusty in the first match, but if he gets through that he's good again.

"For Andy I have no doubts that he'll be in great shape because he has been already."

Federer starts his campaign against Jo-Wilfried Tsonga on Sunday evening, while Nadal gets the singles tournament going that afternoon. Murray meets David Ferrer on Monday afternoon.

The players are in two groups of four and the top two in each group goes through to the semi-finals. The final will be played on November 27.