Ireland's Grand Slam chances were dealt a blow yesterday when Chris Farrell was ruled out of the clashes against Scotland and England after damaging his knee ligaments in training.
The Munster man was centrally involved in yesterday's open session at Lansdowne Road when he went down injured.
Although Joe Schmidt expressed his hope that the 24-year-old would be fine, Farrell later went for scans which revealed the extent of the issue and he is now in a race to be fit for Munster's Champions Cup quarter-final against Toulon and will play no further part in the Six Nations after his man-of-the-match performance against Wales.
Farrell himself was standing in for Robbie Henshaw who suffered a serious shoulder injury against Italy and the latest injury - added to the long-term absence of Jared Payne - leaves Schmidt short of midfielders with Garry Ringrose, Rory Scannell and Sam Arnold also in the frame to partner Bundee Aki.
Ringrose is the favourite to step back into the No 13 jersey after making his return from an ankle injury for Leinster in their win over the Southern Kings last Friday.
He was expected to play against Scarlets this weekend, but Schmidt will now consider whether that is too great a risk given the lack of midfield cover.
Schmidt faces a similar dilemma with Joey Carbery who is light on game-time but may again be held back from Leinster duty after leading the backline in training yesterday.
The coach is hopeful of having hamstring victims Tadhg Furlong and Iain Henderson back for the Scotland clash after they missed the win over Wales, while he played down fears over Conor Murray and Johnny Sexton's injuries.
Murray trained on his own yesterday, while Sexton was not on the pitch at all.
Henderson and Furlong were joined by Rob Kearney and Aki on the sidelines.
The Ireland squad broke up after yesterday's session and will re-assemble on Sunday night to begin preparations for the Scots.
Ireland have announced that Chris Farrell is 'unlikely' to play in the rest of the Six Nations after being sent for a knee scan following a training ground injury this afternoon.
The big freeze was beginning to make itself known as Joe Schmidt put his players through their paces as snow fell on the Aviva Stadium, but afterwards there was a notable thawing in the head coach's approach to his press conference beneath the West Stand.