Nadal withdraws before quarter-final at Paris Masters with knee injury

World number one Nadal through to last eight of Paris Masters

"It is not about London, it is about the longer term" he added. The Serbian now moves into the semifinals for not only his first-career Masters 1000 semifinal, he will now move into the top-50 to end the season after starting the year ranked outside the top-200.

Floridian Isner called the trainer on twice as he beat Juan Martin del Potro 6-4, 6-7 (5), 6-4 in the quarterfinals Friday, but he insisted he is fit to face Serbia's Filip Krajinovic - who progressed thanks to Nadal's withdrawal -- on Saturday.

Nearly nothing could separate the rivals in the shortest and longest points but Nadal had a slight advantage in the mid-range rallies, despite hitting a lot of unforced errors.

Rafael Nadal's fantastic season stalled unexpectedly when the Spaniard injured his right knee during the ongoing Paris Masters.

The world number one had his right knee strapped during his third-round win over Pablo Cuevas on Thursday and struggled with his movement.

Conversation soon went onto the demands of the year-long ATP schedule, the increasing number of cases of high-profile players taking an extended break from the tour and whether changes need to be made to the scheduling of tournaments in the ATP calendar.

It handed the world No 1 spot to Rafael Nadal on a plate - he needed just one win to guarantee it - although things took an interesting twist today.

If Nadal pulls out of the Tour Finals, it would leave world No. 2 Roger Federer as the only member of the "Big Four" - which includes Novak Djokovic and Andy Murray - in the event.

"I am going to do my treatment and my best to be playing in London".

"I have to pull out. I need to play well, but as I say, I hope to be ready to make that happen", remarked Nadal.