Andy Murray has withdrawn from the ATP World Tour Finals due to a groin injury.
The world number three picked up the problem in practice the week before the season-ending tournament and was told to take a seven-to-10 days off.
However the Scot opted to play in London, going down in straight sets to Spaniard David Ferrer in his opening match on Monday afternoon.
He required treatment on the injury during the 6-4 7-5 loss and has now decided not to risk any further damage, meaning his 2011 season has come to a disappointing end on British soil.
Disappointed
"I just didn't have enough time to recover," Murray said at a press conference on Tuesday afternoon.
"I was just disappointed because I knew in my head I wasn't ready to play and wasn't right to play.
"I never want to pull out of tournaments, especially one of this size. But it's a decision I kind of had to make because I was probably going to do myself more damage.
"It might seem like it's a long time away but the Australian Open is six, seven weeks away.
"I could mess up my preparation for that, for the beginning of the year. That off season is so important for me and has been for the last few years of getting myself in shape.
"It's one of the few times when you can have an actual training block."
Janko Tipsarevic will take the Scot's place in Group A - the Serbian's first outing will be against Tomas Berdych on Wednesday before he then faces compatriot Novak Djokovic two days later.
"I feel sorry for Andy for not being able to finish the tournament in his home city," Tipsarevic told Sky Sports.
"But it's an opportuntity which I've got and I'm really happy for it. I hope I can make the best of it.
"When I came, I had in my mind the idea that I would play. That's the only way that you're going to have the mental sharpness you need on the court if the chance is given to you."