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 help me at all to play at my best, nor my rivals of course,” he told the Spanish newspaper ABC in an interview published on Saturday.

“I don't understand why the (event) has to be indoors when you qualify on an outdoor surface.

The world's top eight players will compete in the round-robin end-of-season ATP World Tour Finals in London from Sunday.

Nadal crashed out of the prestigious event last year in the group stage after losing all three of his matches.

Dramatic turn

But since then his career has seen a dramatic about-turn.

The 24-year-old Spaniard regained the World No. 1 spot from Roger Federer after winning three successive Grand Slam titles. “The truth is that it has been an unforgettable year,” Nadal said. — AFP

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