The experienced Munster back rower, who played for Ireland against Australia and Fiji last month, had a scan on Monday and was operated on in a Dublin clinic on Tuesday.
Leamy has been in the wars of late. He sustained an ankle injury during Ireland's recent win over Fiji and had to be carried off the pitch. That injury turned out not to be as serious as feared but he was unable to feature against South Africa.
This latest injury is a desperate blow for the Tipperary man who, given his recent good form, looked set to play his part in Ireland's RBS 6 Nations title defence which begins in February.
It also continues Munster's poor run of luck with injuries this season, with Leamy joining his provincial and Ireland team-mates, Marcus Horan and Jerry Flannery, on the sidelines.