Eight-time Grand slam winner and American legend Andre Agassi believes that Roger Federer is the favourite to win the ATP World Tour Finals as Rafael Nadal does not do well late in the year because of "wear and tear".

Nadal has had a brilliant 2017, winning six titles, which include two Grand Slams – the French and the US Open – and has recently confirmed his place as the year-end world number one for the fourth time in his career. Federer has won seven titles this year, including the Australian Open and a record eighth Wimbledon title to overtake Pete Sampras' seven championship wins at SW19.

Federer, the 19-time men's singles Grand Slam champion, had made fitness his main priority for 2017 and stuck to a limited schedule. He has played just 53 games this campaign compared to Nadal's 77.

Agassi believes Nadal's whirlwind style will be hard to maintain this late in the year, giving Federer a massive advantage. Nadal is still calibrating the risk involved in participating in London after an injury scare, which saw him retire prematurely from the Paris Masters in the quarter-finals last week.

"Historically, Rafa's end of the year is never quite the same as the middle or the beginning. A lot of that goes into the wear and tear and the intensity that he brings to the table [each match]. Who knows with Roger. In a lot of ways he wasn't himself at the US Open and leading up to it. He's taken his time and has proven to be a person that makes pretty good decisions. I do expect him to be at his best." Agassi told ESPN.

Agassi also touched on Federer's possible retirement but said one does not know when one's body gives up. The Swiss has already confirmed his plans for 2018, during which he wants to play in the French Open.

"The one thing I can tell you about the end of someone's career is when it comes, it comes fast. But he's certainly proving that we can't predict when it's coming. Unfortunately, though, at some point we're going to have to say goodbye to someone who has been so great for the game," he added.

Roger Federer and Rafael Nadal
Roger Federer and Rafael Nadal face each other in London Getty Images