Roger Federer has admitted that he is motivated to end his 2015 season on a positive note as he prepares for the ATP World Tour Finals in London.

Federer, a six-time winner of the end-of-season competition, was forced to withdraw from last year's final through injury and has not won the event since 2011, but the Swiss has said that he is "really excited" ahead of the tournament, which starts on Sunday.

The 34-year-old told the official ATP Tour website: "I haven't had issues being motivated for this tournament. I looked forward to it and as it was a priority I played better.

"The idea of playing fellow top-10 rivals gets me going, gets me really excited. I don't relax on making it to the Finals, then go out and lose three crushing defeats. I don't want to finish the year that way."

Federer starts his campaign with a match against Tomas Berdych on Sunday night.