Tadhg Beirne will require surgery after he suffered a fractured ankle in Munster's defeat to Saracens on Saturday.
Munster have been counting the cost of their losses, with four Ireland internationals among those injured at Allianz Park.
Beirne left the pitch on a stretcher, holding a gas and air mask and with his lower left leg in a protective cast after suffering his injury in the opening ten minutes. He will now be ruled out of action for an extended period of time.
Captain Peter O'Mahony, who pulled out with a groin injury during the warm-up, sustained a low-grade adductor injury.
John Ryan, who was withdrawn during the first half with a calf strain, "will undergo his rehabilitation with the medical department", according to a Munster update.
Andrew Conway will follow the return to play protocols after failing a head injury assessment.
“I haven’t spoken to (Beirne) but it looks pretty serious,” said Munster head coach Johann van Graan on Saturday. “Losing John Ryan, which looks also like a pretty serious calf injury and losing Peter (groin) in the warm-up and Andrew Conway to an HIA was tough to take.”
Of O’Mahony, van Graan added: “It’s difficult to say. He pulled out, he had started the warm-up pretty well but pulled out with his groin.
"It’s very frustrating to lose your captain in the warm-up, especially for a game like this. Then to lose Tadhg, your other loose forward, it made the lineout very interesting from our side.”
In better news, loosehead props Dave Kilcoyne (calf) and Jeremy Loughman (ankle) will return to squad training this week.
Joey Carbery will continue to rehab his ankle injury, alongside other continuing absentees Tyler Bleyendaal (neck), Rhys Marshall (knee), Ciaran Parker (calf), and Darren Sweetnam (hamstring).
Munster face an imposing run of fixtures over the coming month, with three interprovincial ties against Connacht, Leinster, and Ulster followed by their final Champions Cup pool games against Racing 92 and Ospreys.
The province is only permitted to play its remaining World Cup squad members once over the coming three games.
“They have to rest most of the time for two weeks consecutively,” said van Graan. "That’s the thing about sending our guys to the World Cup, they’re going to be out for most of these three weeks, and then if you add those injuries...
“We’re facing Connacht away and we’re facing Ulster away, and we’re facing Leinster at home, so it is going to be a huge challenge on our squad and our academy.”
Limerick-based referee Andrew Brace will take charge of Munster's clash with Connacht at The Sportsground on Saturday, with George Clancy the man in the middle for Ulster's visit to Leinster on Friday.