Tadhg Furlong appears to have lost his race to be fit for Ireland's pivotal clash with Wales on Saturday with Andrew Porter set to get his first Six Nations start in the pivotal fixture.
Furlong pulled his hamstring in the early stages of the win over Italy two weeks ago and has not trained fully since.
The tighthead prop took a limited part in the session at the team's Kildare base yesterday and assistant coach Andy Farrell said he was progressing well - but added that the management will not risk him against Wales if he is not fully fit.
And the Irish Independent understands they will err on the side of caution by picking Porter, with John Ryan in reserve.
The loss of the influential Lion is a major blow to Ireland's chances, even if Ireland have improved their depth in the tighthead ranks.
Ryan is the more experienced of the two and was Furlong's regular back-up last season and started three games on tour last June, but he has fallen behind Stephen Archer in the pecking order at Munster this season and conceded a penalty at a pivotal moment of the France game.
At 22, the powerful Porter is clearly being earmarked for big things by the coach and he impressed when he came on after just three minutes against the Italians. However, this would just be his fifth senior start on the tighthead side having switched from loosehead last year.
"It can't be a risk, he has to be fully fit," Farrell said of Furlong.
"Bracket them both (Ryan and Porter) together and we are in a tremendous space. I don't think we can lose really, the more time these guys the get the closer they will get to be the class international players that they want to be."
James Ryan is set to start having recovered from his hip injury and a decision on Iain Henderson's involvement will be taken tonight after his training was also limited by a hamstring issue.
Wales yesterday recalled Lions Dan Biggar, Liam Williams and Leigh Halfpenny to their starting XV for what Warren Gatland described as a "must-win" game.