Leinster back-row Sean O'Brien has been ruled out for the rest of the season and Ireland's summer tour of South Africa.
O'Brien injured his hamstring against France during the Six Nations and suffered a setback last week.
Leinster coach Leo Cullen said that O'Brien will now need surgery and will be out of action for "a considerable period."
Cullen told the club's website: "Sean O'Brien is going to see a specialist in the UK again on Friday, so the likelihood is he's going to have surgery on that hamstring, which would rule him out for a considerable period.
"I'm not sure how long, we'll get the update after the procedure.
"He had the high hamstring tear and there were still fibres intact. Guys have been able to rehab back without surgery from similar injuries.
"Other guys have had that complete rupture where they've gone for the surgical route straight away. It was slower to heal than we would have liked, he was getting close and putting in his rehab, but just broke down at that stage.
"We sought out a few opinions at that stage and he's going down the surgical route now which is frustrating for all."