Ireland captain Rory Best must shake off a stomach bug if he is to face Italy in Rome in Saturday's Six Nations showdown.
Hooker Best missed Ireland's captain's run at the Stadio Olimpico on Friday, instead remaining at the team hotel in a bid to beat his illness.
Niall Scannell would start should Best fail to recover, with James Tracy likely to fly out to join the squad as cover.
Ireland remain confident Best will be fit to start, and could leave a decision on their skipper's fitness until Saturday morning.
"Rory has had a bit of a stomach upset overnight, he didn't sleep particularly well," said forwards coach Simon Easterby.
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"So we've left him to rest. You can't predict that, but we've left him back in the hotel when we did the team run.
"We're confident that he will recover in time for tomorrow."
Ireland may now have to hunt their first win of the campaign without their 101-cap skipper.
Joe Schmidt's men lost out 27-22 in Scotland last weekend, and only victory in Rome will keep their slim title chances alive.
Vice captain Jamie Heaslip would take the armband in Best's absence, but Ireland are clearly giving the 34-year-old every chance of recovering.
Ireland entered the Six Nations without 56-cap hooker Sean Cronin after he was ruled out of the tournament with a hamstring problem.
That has opened the door for the uncapped Scannell to step up, and the 24-year-old from Munster remained an unused replacement in Scotland.
Tracy made a try-scoring Test debut in Ireland's 52-21 victory over Canada in Dublin in November.
The 25-year-old was initially overlooked for selection for Ireland's Azzurri clash, but was later omitted from the Leinster squad to face Treviso in Italy on Sunday.
