Neil Cronin has suffered an anterior cruciate ligament injury in training for Munster while a neck problem is likely to rule hooker Niall Scannell out for two months.
Scrum-half Cronin, who featured for 21 minutes as a replacement in the last-gasp victory over Scarlets at the weekend, suffered the injury in Monday's training session.
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The 27-year-old is now looking at an extended period of time on the sidelines, joining new signing RG Snyman on the long-term casualty list.
Hooker Scannell is set to be unavailable for "approximately" two months from a neck injury picked up last week, while Chris Cloete (neck) and Keith Earls (back) continue to work their way back to full fitness.
There was better news for Conor Murray (thigh) and Shane Daly (groin) with both players expected to train this week.