Ireland winger Keith Earls will be out of action for up to six weeks after injuring a knee in Munster's Pro12 defeat by Leinster.
Earls, who can also play at centre or full-back, suffered the injury in the first minute at the Aviva Stadium.
The 24-year-old is set to miss the Heineken Cup meetings with Northampton and Castres and league meetings against Edinburgh and the Ospreys.
He will also be a doubt for a European double-header against the Scarlets.
A Munster statement read: "Keith Earls had a scan in Limerick that confirmed he has sustained medial ligament damage and will be out of action for four to six weeks."