Rua Tipoki is out of the final games in the Pool stage after rupturing his hamstring in the Magners Legaue defeat to Ulster last weekend.
The Kiwi centre, who was so instrumental in Munster's European success last season, will be sidelined for four weeks.
And flanker James Coughlan damaged a shoulder after coming on as a replacement in the second half and he is also ruled out for four weeks.
Ronan O'Gara also suffered a hamstring injury but it's not as serious as first thought although he remains a doubt for the trip to Wales.
Burt better news for coach Tony McGahan is that club doctors report Paul O'Connell, Denis Leamy and Tomas O'Leary will be fit and available for a place in the squad for this weekend's top of the table league clash with the Ospreys.