World number one Roger Federer said he is hoping to be fit in time for next month's Tennis Masters Cup, after pulling out of the Swiss Indoors tournament with a ruptured thigh muscle.

Speaking at a press conference just hours after withdrawing from the event in his home city of Basel, Federer said he had been told by doctors to rest for a period of ten to 14 days.

"It's a huge, huge disappointment for me, obviously," said Federer. "I've been to this tournament many, many times -- both as a player and as a ballboy -- and I really thought I had a big chance to win this year. I thought my preparation had been perfect."

The 23-year-old, who has won the Australian Open, Wimbledon and U.S. Open Grand Slam titles this season, said he had first felt pain in his left thigh during a practice session on Monday.

When the pain returned on Tuesday, he consulted doctors before undergoing an MRI scan at a nearby hospital.

The result from the scan forced Federer to pull out of the tournament, just hours before he was due on court for his opening round match against Peru's Luis Horna.

Ironically Horna himself was later forced to retire with lower back pain after stepping on court to face Federer's replacement, Czech lucky loser Bohdan Ulihrach.

MASTERS CUP

As well as missing out on his home tournament, Federer conceded that he was now almost certain to miss next week's ATP Masters Series tournament in Paris.

However he said he would be doing all he could to be back in time for the lucrative season-ending Masters Cup which begins in Houston on November 15.

"If necessary I may even fly earlier than I'd planned to Houston, to try and be 100 percent fit for the start," he said.

Regardless of whether he makes it to Houston, Federer is already guaranteed to finish the year as world number one.

His withdrawal from Basel leaves Britain's Tim Henman, the world number four, Olympic champion Nicolas Massu of Chile and the world number 10, David Nalbandian of Argentina, as the leading contenders for the title.

"It's one of those things that's not in our power," tournament president Roger Brennwald said. "The important thing is that Roger gets fit again."

Fifth seed Tommy Robredo of Spain came close to following Federer out on Tuesday after facing a scare in his first round match against Swiss wildcard entry Stanislas Wawrinka.

Wawrinka, the junior champion at last year's French Open, led Robredo by a break in the third set before the Spaniard fought back to win 7-6, 5-7, 6-4.

In Tuesday's other first round action, Argentine eighth seed and French Open champion Gaston Gaudio booked his place in the second round with a 7-6, 6-4 win over Belgian qualifier Dick Norman.