Debutant Milos Raonic has withdrawn from the ATP Finals with a quad injury ahead of his final round-robin match against Japan's Kei Nishikori.

The seventh-seeded Raonic, who lost his first two matches in Group B in straight sets, will be replaced by Spain's David Ferrer, the first alternate at the year-end tournament.

Raonic said ''as badly as I wanted to play, you've got to be at the top of your game here and I couldn't be close to that today. Wouldn't have been fair to the fans if I had played a mediocre match or had to stop.''

Six-time champion Roger Federer will take on Andy Murray in the group's other match. If the 17-time Grand Slam champion beats Murray and Nishikori defeats Ferrer, then the Scot will be eliminated from the indoor event.

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