PARIS (Reuters) - World number two Roger Federer was confident he would take part in the season-ending Masters Cup despite pulling out of the Paris Masters Series event with a back injury on Friday.
"I got to do all sorts of different checks and stuff. But usually the back is something that takes a few days and it's better again," the Swiss told reporters after handing American James Blake a walkover into the semi-finals.
"I've had a lot of back pain over all the years of playing tennis, so it's not like the first time. It's just the first time it's acute during a tournament and it makes me pull out. I'll check it out for the next few days."
Despite the setback, Federer said he expected to defend his title in Shanghai. The tournament begins on Nov 9.
"The flight is scheduled for Monday. I hope I can recover ... otherwise I'll postpone that. I'm confident and I'm positive that hopefully it's going to get better in the next few days."
Federer said he first felt the pain in his back during his second-round match against Swede Robin Soderling.
"On a serve I just felt something sort of really stiffening up in my back, (but) played through it. I took painkillers there," he said.
"Then against (Marin) Cilic yesterday I had to run for a forehand in the second set. The last few games of the match I really had to sort of just like change my positioning for returning and change my serve.
"So I felt that something was bad but I expected to get better overnight, which I always have done.
"I can't take a chance over a back, so I just want to play it safe and then hopefully be fine for Shanghai again."
Federer's withdrawal in Paris means the Swiss has failed to win a regular Masters Series event this year for the first time since 2003.
He has had an under-par season, losing his Wimbledon crown and world number one spot to Spaniard Rafael Nadal, who also beat him in the French Open final.
(Reporting by Julien Pretot, Editing by Pritha Sarkar)