World number three Andy Murray has withdrawn from the ATP World Tour Finals with a groin injury.
The 24-year-old aggravated the complaint during his loss to David Ferrer yesterday afternoon.
"It's just a really difficult decision to make because it's one of the best tournaments in the year to play and it's something that you also work all year to play here, as well," said Murray.
"There was no real positive sort of coming out and playing because yesterday I was really unhappy on the court.
"I couldn't give anywhere near my best, so that's what was disappointing. It would probably do myself more damage by playing than not."
Murray's place in the tournament has been handed to Serbian and world number nine Janko Tipsarevic, who will make his debut tomorrow against Tomas Berdych.