Jonathan Sexton could miss the rest of the Ireland's Six Nations Championship due to a thumb ligament injury.
The fly-half's French club Racing Metro confirmed the 28-year-old will miss between 10 days and six weeks with the thumb problem he suffered in the 13-10 Six Nations defeat to England.
Ireland host Italy in Dublin on Saturday, March 8 before closing their Six Nations campaign with a trip to France a week later.
"Johnny Sexton returned from Twickenham with a thumb ligament injury, and will be unavailable between 10 days and six weeks," said Racing Metro coach Laurent Labit.
However, the Irish Rugby Football Union later released a statement which insisted the injury was not as bad as feared.
It said: "The Ireland medical team have had a consultant hand specialist review Jonathan and his scans.
"The ligament damage sustained does not warrant surgery and if Jonathan continues his current rate of improvement we would be confident that he will be available for selection against Italy."
Sexton left Twickenham on Saturday with his hand in a splint, Ireland head coach Joe Schmidt had revealed on Monday.
Schmidt and Ireland's medics had remained hopeful the former Leinster fly-half would battle past his injury in time to line up against Italy in Ireland's penultimate Six Nations clash.
But now it looks as though his chances of aiding Ireland's push for the Six Nations title are slim at best.
Sexton returned to France after Ireland's slender defeat to England, with Racing expecting him to face Castres in Top 14 league action this weekend.
His Paris club have ruled him out of action, though, and cast his Six Nations into doubt in the process.
Ireland boss Schmidt admitted on Monday he may have looked to rest Sexton against Italy even if he found fitness, in order to keep squad players sharp.
Now the Ireland boss is likely to turn to Ulster's Paddy Jackson to lead the backline against the Azzurri, with Leinster's Ian Madigan the potential understudy.
Ireland's defeat at England on Saturday leaves the Six Nations title locked in a four-way tussle.
England, Wales and France can all still claim the crown, with Ireland also eyeing glory should they see off Italy and the French in Paris on the final weekend.
Ireland boss Schmidt rates England as favourites for the title, though, despite the four contenders all having lost one clash in three rounds.
"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.
"I see their flanker Zanni has signed for Castres for next year, and they are very good players.
"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.
"Italy had a lot of the game against France, they were right in the game against Cardiff and they will feel fairly shattered to lose to Scotland, to lose to a last-minute drop-goal.
"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."