Andy Murray of Britain attends a news conference at the ATP World Tour Finals at the O2 Arena in London, Nov 22, 2011. [Photo/Agencies]

* Serbia's Tipsarevic comes in as replacement

LONDON - The best season of Andy Murray's career ended in anti-climax when he was forced to withdraw from the ATP World Tour Finals with a groin injury on Tuesday.

Briton Murray had laboured to a 6-4 7-5 defeat in his opening Group A match against Spain's David Ferrer the previous day, after which the world number three revealed that he had damaged his groin while practising for the prestigious eight-man tournament at London's 02 Arena.

He failed to keep his allotted booking on the practice court on Tuesday and after consulting with his team the 24-year-old Scot decided to pull out of the tournament rather than risk further injury.

"It was one of those things where you kind of hope that things are going to get better, but the reality was that wasn't ever going to happen," a glum-looking Murray told reporters.

"Yesterday I was really unhappy on the court. I wasn't enjoying it at all. I couldn't give anywhere near my best."

On-site alternate Janko Tipsarevic of Serbia will take Murray's place for the final two group matches against Tomas Berdych on Wednesday and world number one Novak Djokovic on Friday, and will inherit the Briton's record so far.

The injury was a cruel blow for Murray who reached the semi-finals of all four grand slam tournaments this year and since the US Open had been the form player on the men's tour along with former world number one Roger Federer.

Before his surprise defeat by Ferrer he was being strongly tipped to win the season-ending tournament which is regarded as just below the majors in terms of prestige.

"I was told I would have to take a week to 10 days off and I just didn't have a chance to recover," Murray, who won three consecutive titles during the recent Asian swing, said.

"I never want to pull out of tournaments, especially one this size. But it's a decision I kind of had to make because I was probably going to do more damage to myself.

"It's disappointing to finish the year that way. You kind of want to go out having given everything, like last year's match (in the semi-final against Rafa Nadal).

One of the main factors behind Murray's decision was the looming Australian Open. He reached the final there this year, losing to Djokovic, and his thoughts are now on making sure he is 100 percent for the start for 2012.

"It might seem to you guys like it's a long time away. But the Australian Open is six, seven weeks away," Murray said.

"I could mess up my preparation for that, for the beginning of the year."

Murray's withdrawal is a blow for the London organisers and the home fans, although with all the evening sessions sold out to their 17,500 capacity and most of the day session nearly full his absence will not affect attendances.

The tournament continues later on Tuesday with a blockbuster clash between Nadal and Federer in Group B - the 26th time they have met in their illustrious careers.