Stomach bug floors Best
Stomach bug floors BestSHARE
Joe Schmidt's men are looking to make amends for last week's shock 22-27 defeat to Scotland at Murrayfield.
But Best could end up having to sit out. He will be monitored over the coming 24 hours at Ireland's hotel in Rome before a decision is made whether he is fit to start.
"Rory has a stomach bug and the best course of action was to leave him back in the hotel," said Ireland's assistant and forwards coach Simon Easterby.
Best was expected to speak to media following the Captain's Run, held 24 hours before kick-off, at the Stadio Olimpico.
"Hopefully he is going to be better with some extra hours of sleep but James Tracy will be joining the squad."
Although Easterby said he is "confident" Best, who was due to earn his 102nd cap, will recover in time, his absence would see Niall Scannell come off the bench and step into the middle of the front row.
"If Rory doesn't come through, Niall will come across," added Easterby.