Donnacha Ryan will miss Ireland's autumn internationals and is in a race against time to be fit for the 2015 Six Nations campaign after Munster announced the lock will undergo toe surgery.
He looks set to miss at least 10 rounds of Munster's Pro12 league campaign.
Ryan missed most of Ireland's victorious Six Nations 2014 campaign through injury, failing to make an appearance despite forcing his way back into the training squads for the England and France clashes.
A Munster Rugby statement said: "Following a consultation with the specialist in London it has been confirmed that Donnacha Ryan will now require surgery on his toe.
"The Tipperary lock injured his right foot in the Pro12 game against Treviso in March, and after extensive, conservative rehabilitation he has unfortunately been unable to rehabilitate the injury fully.
"He will now undergo surgery next week and is expected to be ruled out for the next four to six months."
Munster head coach Anthony Foley said: "Donnacha has done everything that has been asked of him and we know it has been a tough time for him with the option of surgery available as a last resort.
"We are now at that point and we just want him to get through the next stage and back to full fitness."
Meanwhile, Munster's Keith Earls will have his progress in recovering from a knee injury assessed next week, while Tyler Bleyendaal is recovering from a disc lesion operation in New Zealand.