The 24-year-old had been a doubt for the Irish province’s Heineken Cup quarter-final 47-23 win against Toulouse.
Casey is in plaster for 10 days but should be right in a couple of weeks for the semi-final
However, he started the match on Saturday and will have reconstructive surgery today following a scan on Monday to determine the extent of the injury.
O’Mahony lasted just 19 minutes before over-extending his left shoulder—exacerbating an injury which had first become a problem during Ireland’s successful Six Nations campaign—at a lineout.
The Munster star was replaced by birthday boy CJ Stander, who put in a man-of-the-match performance in his captain’s absence.
“O’Mahony travelled to Dublin late yesterday evening for a review with the specialist, and following the consultation it was confirmed that the Munster captain required surgery on his left shoulder,” said a statement on the club’s website.
It means the Corkonian, who had been in impressive form for the national side, will miss Munster’s Heineken Cup semi-final against reigning champions Toulon in Marseille on 27 April.
He will also be absent for their final four matches of the RaboDirect Pro12 regular season and play-offs, and could be a doubt for Ireland’s summer tour to Argentina.
Former All Blacks centre Casey Laulala could return for the European semi-final despite breaking a bone in his right hand as Munster ran in six tries against the four-time Heineken Cup champions.
“Casey is in plaster for 10 days but should be right in a couple of weeks for the semi-final,” said head coach Rob Penney.
In further good news for Penney ahead of his side’s Pro12 clash with Glasgow Warriors on Saturday, lock Donnacha Ryan could return from a foot injury.
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