John McEnroe backs Roger Federer for ATP World Tour title

John McEnroe has already tipped Rafael Nadal to win next year's Australian Open but thinks Roger Federer is the man to beat at the ATP World Tour Finals.

The seven-time Grand Slam champion believes that while Nadal's athleticism favours him over five sets, Federer has the egde in the shorter format at the O2.

"I would pick Nadal if this were the Australian Open because I think he's much tougher to beat in longer matches," said McEnroe, 51. "If he remains healthy he's the guy I would pick for every major right now until proven otherwise. But in the best of three it remains to be seen; I would certainly give Federer more of a chance in a shorter match."

However, former Wimbledon champion Goran Ivanisevic believes the world No1 will take the title to add to the three Grand Slams he's won this season.

"This year Nadal has put a lot of things that he has never won before in his basket," said the 39-year-old, who along with McEnroe is playing on the ATP Champions Tour. "It doesn't matter what surface it is as long as he is fit and playing well."

Former French Open champion Carlos Moya, 34, has retired because of a persistent foot injury.