Andy Murray of Britain reacts during his men's singles tennis match against David Ferrer of Spain at the ATP World Tour Finals at the O2 Arena in London November 21, 2011. Ferrer beat Murray 6-4 7-5.  [Photo/Agencies]

LONDON - Andy Murray could pull out of the ATP World Tour Finals after just one match because of a groin injury, the Briton said on Monday after slumping to defeat against Spain's David Ferrer.

The world number three suffered a first defeat on a surface other than clay against the tenacious Ferrer, losing 6-4 7-5 at the O2 in his opening Group A match.

He required treatment after losing the first set and the 24-year-old looked gloomy when asked about his chances of continuing in the season-ending showpiece.

"Yeah, I mean, I had a problem with my groin. I have to see how it goes for tomorrow," Murray, who arrived in great form after a recent 17-match winning streak that included three consecutive titltes in Asia, told reporters.

"I'll decide tomorrow whether or not I keep playing. If it wasn't slams or this event, I wouldn't have played."

After losing in straight sets Murray would probably have to beat world number one Novak Djokovic and Czech Tomas Berdych to reach the semi-finals, although the mathematics of the tournament's format mean he could progress with one win.

Should he fail to recover in time for his second match, either against Djokovic or Berdych on Wednesday, Serbia's Janko Tipsarevic would fill in as the first alternate.

"I didn't know exactly how it was going to feel on the court today. I haven't been able to do too much training this week," Murray, who sustained the injury in practise, said.

"I felt flat, in the second set especially. I don't know whether how I was feeling contributed towards that.

"I can decide until one minute before the match on Wednesday if I want to (pull out). So, I'll see how I feel tonight and tomorrow and decide."