Munster will have to go into their back-to-back Pool 1 clashes with fellow unbeaten RaboDirect PRO12 side the Scarlets without the services of All Blacks legend Doug Howlett.
The flying wing, who helped the Irish province lift the Heineken Cup for a second time at the Millennium Stadium in 2008, damaged his Achilles tendon in the 19-13 league defeat to the Ospreys at the Liberty Stadium at the weekend.
A Munster statement said: "Doug Howlett will have a scan and see a specialist early this week to determine the exact nature of the injury he sustained against Ospreys. Initial examination suggest he's damaged his Achilles tendon and he has definitely been ruled out of Munster's upcoming Heineken Cup matches against Scarlets."
Munster travel to Parc y Scarlets for the first leg of the top of the Pool clashes on Saturday. They are currently one point behind the Scarlets.
The home side picked up an injury scare of their own at the weekend when teenage wing Geroge North limped off at the end of Wales' 24-18 defeat to Australia. The Scarlets had five players in the Wales 22 and another, centre Jonathan Davies, missed the game with a groin problem.