Sean O'Brien could miss Ireland's Test matches in November as he needs surgery on a persistent hip injury.
The Leinster flanker will have the operation in the near future and is expected to be out for around 14 weeks.
It means he will not be back in training until at least mid-October, leaving him little time to be fit for Ireland's opening match against South Africa on November 10.
The 25-year-old has struggled with the problem all season, meaning he has had to restrict his training in order to be fit to play for both club and country.
Ireland manager Mick Kearney confirmed: "He is going having some keyhole surgery on his hip to repair some cartilage damage.
"It's going to happen within the next week or so and the recovery period for this type of operation is 13 to 15 weeks. It means it could be up to four months.
"Obviously it's going to make him doubtful for the November series."
O'Brien will miss the opening rounds of Leinster's PRO12 campaign and the first two rounds of the Heineken Cup in October.
It comes as part of a triple blow for his club side Leinster, after it was revealed that David Kearney and Rhys Ruddock were also facing similar lay-offs.
"Dave has had a similar kind of procedure done and Rhys I think is having a similar type of procedure," added Kearney.
"It seems to be a more common type of injury than heretofore. I'm not sure the reason why. People are a bit mystified by it."
"Full recovery is expected but I suppose, like any operation, there is always some risk attached to it."