Ireland's medical team and the Paris club Racing's management hold conflicting opinions over Sexton's chances of a quick return from the thumb ligament damage he suffered in Saturday's 13-10 defeat to England at Twickenham.
Sexton's French club ruled the 28-year-old playmaker out of action for between 10 days and six weeks on Thursday in a tweet posted by coach Laurent Labit.
It's a timescale that could all-but end his Six Nations action.
Ireland bosses later issued a statement rejecting concerns Sexton was already out of contention to face Italy in Dublin on Saturday, 8 March.
The IRFU quickly responded with a statement of their own however, claiming Sexton could yet be fit to face the Azzurri.
"The Ireland medical team have had a consultant hand specialist review Johnny and his scans," read the IRFU statement.
"The ligament damage sustained does not warrant surgery and if Johnny continues his current rate of improvement we would be confident that he will be available for selection against Italy."
Ireland are locked in a four-way fight for the Six Nations title, and losing chief back line architect Sexton would be a major blow.
The squad have been training in Belfast over the last few days.
Brian O'Driscoll took part on Thursday, doing some additional work on the bike to ease the cramping in his calf which has been troubling him.
Head coach Joe Schmidt's men travel to Paris to face France in their final fixture on Saturday, 15 March, a week after hosting the Italians.
England, Wales, France and Ireland have all lost one of their three matches in the tournament so far.
Ireland could claim their first title since their 2009 Grand Slam with two more victories.
This latest twist in Sexton's onrunning club-versus-country saga does little to ease the tug-of-war over the former Leinster outside-half that has raged since his move to France last summer.
Schmidt admitted Ireland had "lost control" of Sexton during the autumn Test series, when the star playmaker suffered a hamstring strain on club duty in the middle of the November international schedule.
Sexton left Twickenham on Saturday with his hand in a splint, Schmidt had revealed on Monday.
The 41-cap fly-half returned to France after Ireland's slender England defeat, with Racing expecting him to face Castres in Top 14 league action this weekend.
His Paris club have since ruled him out of action though, and cast his Six Nations into doubt in the process.
Despite Ireland's clear chances of Six Nations glory, Schmidt still rates England as title favourites.
"I think England are going to be the toughest team to beat without a doubt," said Schmidt, warning Ireland to be extremely wary of Italy's threats.
"One of the problems for us is making sure that Italy is our full focus and that it stays that way over the next few days and next week.
"They have a very experienced, very powerful front-row and with Sergio Parisse at number eight he's one of the world's best anchoring that set-piece.
"Across the board I don't think we'll get anything easy against Italy.
"There's a real danger that there's an expectation we'll put a 10 or 20-point margin on them.
"All we want is a margin that gives us the two points for the win, and that will be tough enough.
"Ireland lost to them last year, France lost to them last year: there's a real danger in us looking too far forward.
"We've got to put ourselves in the position to be able to win the championship, and the only way we can do that is to beat Italy first and foremost."