Leinster flanker Sean O'Brien is set to meet with a specialist on Friday when it's likely he will be scheduled for surgery on his hamstring.
After naming his squad for their PRO12 semi-final against Ulster, head coach Leo Cullen gave an update on the powerful back-row star.
"Sean O'Brien is going to see a specialist in the UK tomorrow," he told Leinster's website.
"The likelihood is he's going to have surgery on that hamstring, which will rule him out for a considerable period. I'm not sure exactly how long, we'll get the update post the procedure.
"Guys have had similar injuries and been able to rehab back to play without surgery. Other guys have had that complete rupture where they've gone for the surgical route straight away. He was getting close to the stage where he was pushing on his rehab and he just broke down. He sought out a few different opinions since, so he's going the surgical route now.
"It's frustrating for all. He's been such a key figure in all the good things in Leinster and with Ireland as well. We'll do all we can do to get him back to those levels again."
Cullen also offered an update on international loosehead prop Cian Healy, who, like O'Brien, misses this Friday's showdown with Ulster.
"It's unlikely that Cian will feature this season. He's just being assessed all the time. Apologies if that comes across as vague, but the reality is we're just trying to get a really good plan for him. We're assessing him on a very regular basis," said Cullen.
"He had a surgical procedure this time last year on his neck. It's just taken time to come back. To complicate matters a little bit further, he's also been carrying an issue with his knee. He's on a really good course of action for that. We're just managing those guys as best as we possibly can."