Cian Healy will miss Ireland's autumn internationals and is in a race against time to be fit for the Six Nations after being ruled out for up to five months following hamstring surgery.
He will also miss all of Leinster's European Rugby Champions Cup pool games.
The Leinster prop was injured was injured in training this week and the province's coach Matt O'Connor confirmed on Friday night that his absence would be long-term.
"Cian had surgery today on a hamstring, it was a lot worse than we first thought,” O'Connor told RTÉ Sport after Leinster's 37-23 win over the Cardiff Blues. "He’ll be sort of four or five months out."
“We didn’t know how significant it was and they’ve had to repair the hamstring, so that’s the time frame they’re talking about at the moment.”
A five-month recovery period would rule Healy out of Ireland's Six Nations clashes with Italy and France.