O'Driscoll limped off in the 75th minute of Saturday's 16-12 RBS 6 Nations defeat by Wales after being hit by a tackle while stripping the ball on the ground.

It was initially thought the Leinster centre would be sidelined for up to two months but tests revealed the damage was not as severe as first feared.

An Irish Rugby Football Union statement read: "A scan on Brian O'Driscoll's left hamstring this afternoon has confirmed the presence of a moderate tear.

"The injury is not as bad as was first feared and it is expected that this will prevent him from playing for a period of between three and four weeks."

Leinster currently top the Celtic League and the news means O'Driscoll will be available for the title run-in - possibly in time for the home clash with Munster on April 12.

The 29-year-old has already been ruled out of Ireland's RBS 6 Nations finale against England but will return well before the summer tour to New Zealand and Australia in June.

O'Driscoll's absence has left Ireland without their first-choice centre partnership against England as Gordon D'Arcy is already missing because of a fractured forearm.

Ireland name their team for Twickenham - a happy hunting ground during the last two visits - at lunchtime on Tuesday.

Coach Eddie O'Sullivan has indicated that the Irish Rugby Football Union will decide what approach to take at Twickenham, although his innate conservatism ensures his recommendation involves his tried and tested.

"Whether I experiment against England depends on what the union wants," he said.

"There’s one game left in the 6 Nations and you don’t make strategic changes likes that in a middle of a tournament. You don’t base it on winning or losing one match.

"I’ve always been told that whatever it takes, go out there to win every game. That’s the job.

"No-one has come to me and said we’ll see how things go. If you want to throw a few young players on at Twickenham don’t be afraid of it.

"You can go that road but that’s not the way the IRFU see it. Every other Ireland coach has been in the same position.

"In my opinion, you pick your strongest team and try to get the best result.

"There's more latitude to change things around during the summer tour but we have to finish the 6 Nations as strongly as we can.

"We can’t just go willy-nilly into Twickenham."