Rafael Nadal has withdrawn from the ATP Finals after being severely hampered by his knee injury during a three-set defeat to David Goffin.

Goffin beat the limping world number one 7-6 (7/5) 6-7 (4/7) 6-4 at London's O2 Arena and, after the match, Nadal announced he would be pulling out of the tournament.

It is the sixth time Nadal has withdrawn from this competition in 13 years of qualifying and he will now be replaced by fellow Spaniard Pablo Carreno Busta.

Nadal's problematic right knee had forced him out of the Paris Masters earlier this month and there was always a question mark over whether he would be fit enough to play at this event.

The 31-year-old fought hard against Goffin and saved four match points in the second set, but he was visibly wincing in the decider when he appeared to be running almost on heart alone.

"I am off. My season is finished," Nadal said less than half an hour after his match had concluded.

"I tried hard. I did the thing that I had to do to try to be ready to play. But I am really not ready to play, no?

"I really fought a lot during the match but knew that there was probably a big chance to be the last match of the season. That's what it is going to be.

"It is not a decision at all, it's about the pain. I cannot hold with enough power to keep playing. I tried, but seriously (it) was a miracle to be very close in the score during the match."