Nadal facing 'most difficult' event of year

World No 1 Rafael Nadal, who has won three successive Grand Slam titles this year, believes the ATP World Tour Finals in London is a much tougher challenge for him.

"To me this is the most difficult tournament of the year. The surface does not allow me to play at my best, nor my rivals of course.

"I don't understand whyu00a0 the event has to be indoors when you qualify on an outdoor surface."

Since crashing out of the prestigious event last year in the group stage Nadal regained the world number one spot from Roger Federeru00a0 winning three successive Grand Slam titles. "I think winning in Monte Carlo was decisive.

I had gone a long time without winning, many months without taking a title, and it was very important to me. It gave me the reassurance I needed."

Winning the French Open on his favourite clay court surface was also "vital because I had knee problems, and was generally having a hard time.

The truth is that it has been an unforgettable year and I'm very, very happy for everything that has happened. I am excited at times and now I want to finish as best as possible."u00a0