Best, who is set to win his 102nd cap in Rome if he recovers, was ordered to rest in bed after being ill overnight.
With Best’s usual deputy Sean Cronin out of the championship, uncapped Munster hooker Niall Scannell is on standby to make his debut.
“It would be absolutely no problem,” said No8 Jamie Heaslip, who would take over the captaincy. “It happened to us with Paulie [O’Connell] in one of our first championships, so if it has to be it has to be.
Rory Best is an injury doubt for Ireland's match against Italy
Jamie Heaslip would take over the captaincy should Best not play against Italy
“We’ve got a really good leadership group and if one guy isn’t there for whatever reason that leadership group gets tighter and really drives the collective.”
Italy captain Sergio Parisse thinks whether Ireland have Best or not Italy will need another “miracle” on a par with November’s triumph over South Africa to win.
The Azzurri slumped to a 33-7 home loss to Wales to open their campaign last weekend, a result which left the perennially outstanding Parisse with the unenviable record of being the most defeated player in Test history. And he expects an even tougher challenge from Ireland.
Six Nations 2017: 10 weird and wonderful highlights from past tournaments
Fri, February 3, 2017
Click through the gallery for some of the most bizarre moments in Six Nations history
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Click through the gallery for the most bizarre moments in Six Nations history
“Beating South Africa with the system we have in the country at the moment was a miracle, but it was possible because of the commitment of the players and the staff who believe in us,” said Parisse.
“Ireland are better than Wales, so it’s going to be extremely difficult.
“Ireland are the only team in the Six Nations which is extremely adaptable depending on the opponent. Joe Schmidt is such a clever coach. We know the size of the challenge.”
Italy: Padovani; Esposito, Benvenuti, McLean, Venditti, Canna, Gori; Lovotti, Ghiraldini, Cittadini, Fuser. van Schalkwyk, Mbanda, Favaro, Parisse (capt). Replacements: Gega, Panico, Chistolini, Biagi, Steyn, Bronzini, Allan, Campagnaro.
Ireland: Kearney; Earls, Ringrose, Henshaw, Zebo; Jackson, Murray; Healy, Best (capt), Furlong, Ryan, Toner, Stander, O’Brien, Heaslip. Replacements: Scannell, McGrath, Ryan, Dillane, Van der Flier, Marmion, Keatley, Gilroy.
Referee: Glen Jackson (New Zealand).