Andy Murray of Great Britain reacts during the men's singles first round match against David Ferrer of Spain to the men's singles first round match against David Ferrer of Spain during the Barclays ATP World Tour Finals at the O2 Arena on November 21, 2011 in London, England.

Andy Murray's hopes of winning the ATP World Tour Finals were dealt a double blow when he lost his opening group match to Spain's David Ferrer and then warned he could have to withdraw from the tournament with a groin injury.

"I'll decide tomorrow whether or not I keep playing. If it wasn't slams or this event, I wouldn't have played." said Murray, who sustained the injury in training.

Murray often looked leaden-footed and lacked any spark despite leading in both sets.

The world number three needed treatment at the end of the first set and although he was able to carry on without calling for the physio again, he could find no way through the formidable defences of the 29-year-old from Valencia.

Ferrer conceded that he played about as well as he did in two recent straight-set losses to Murray in Tokyo and Shanghai.

"I played very consistent all the match," Ferrer said. "Maybe the first set I play better than the second. In the second sometimes I was a little bit nervous. In important moments, I take my chance, and nothing else."

Murray, if he does recover, could have to beat both in his remaining matches to qualify for the semi-finals of a tournament that ranks just below the grand slams in terms of prestige and importance.