The severity of Robbie Henshaw's injury should become apparent at Thursday's team announcement but the Connacht centre has not made Joe Schmidt's opening World Cup team to face Canada at the Millennium Stadium on Saturday after pulling up in training this week.
The 21-year-old Athlone man is to be replaced at inside centre by Luke Fitzgerald. While somewhat surprising, the move is not completely out of the blue; Schmidt previously selected the 2009 Lions winger in the position, albeit for Leinster after he failed to make Declan Kidney's 2011 World Cup squad.
Should Henshaw's injury prove more serious than it currently seems – he did travel with the 31-man panel and management to Cardiff on Wednesday night – Leinster's Noel Reid would be next in line for a call-up. Reid has just one cap, from last year's summer tour of Argentina, but Gordon D'Arcy has a shoulder injury.
There is better news in all other areas of the field as
is passed fit to start after some pre-season concerns over his hamstring/knee.
Conor Murray has recovered from the concussion he suffered when he collided with Joe Marler's boot at Twickenham a fortnight back. It was Murray's third head injury inside a year but he is fit enough to link up with Johnny Sexton at halfback.
All told, it looks like Schmidt will name his strongest possible side.
Keith Earls should see off Simon Zebo on the left wing while Iain Henderson will partner captain Paul O'Connell in the secondrow.
Henderson's form for Ulster and off the bench for Ireland during the previous two Six Nations campaigns looks to have eventually removed Devin Toner, despite his huge improvements and obvious lineout advantage.
Otherwise, it is expected to be the same pack that has proved so effective since 2013, with both Jack McGrath and Cian Healy to share time at loosehead prop as Healy plays his first game since neck surgery last May.
But the main concern right now is Henshaw.
IRELAND (possible): R Kearney; D Kearney, J Payne, L Fitzgerald, K Earls; J Sexton, C Murray; J McGrath/C Healy, R Best, M Ross; I Henderson, P O'Connell (capt); P O'Mahony, S O'Brien, J Heaslip.