Dave Kilcoyne has emerged as a major doubt for the Six Nations after injuring his knee during the first half of Munster's Champions Cup win over Castres.
The loosehead prop was due to link up with the Ireland squad in Carton House last night ahead of preparations for the opener against France on Saturday week, but he is now deemed highly unlikely to be fit.
Kilcoyne was picked ahead of Jack McGrath on the bench for both of Ireland's bigger November games against South Africa and Argentina and was in with a shout of being involved in Paris despite the Leinster man's recent good form.
"He's in a bit of pain, a lot of ice around the knee," Munster coach Johann van Graan said.
"I think it will be a bit of time before we know exactly what's wrong. If he stays down it must be serious but I don't want to speculate at this stage.
"He's important to our squad and to Ireland so I hope he recovers really quickly."
Joe Schmidt will be relieved to learn that wing wonder Jacob Stockdale will be fit and available for selection despite limping out of Ulster's defeat to Wasps.
The youngster suffered a dead leg and is not considered a doubt for the championship.
Keith Earls, his nose caked with blood, a plug hanging out of one nostril, a big bruised lump under one eye like something you'd see on a mugging victim, touching down in the left corner at Thomond Park on the foulest day imaginable, might just have scored the most Munster of all Munster tries.