Two-times Heineken Cup winners Munster will be without Irish international scrum-half Tomas O'Leary for up to two months.
O'Leary suffered a thumb injury in Saturday's Magners league defeat to arch-rivals Leinster at the new Aviva Stadium and has been forced to undergo surgery on the injury..
Doctors have predicted a touchline wait of between six and eight weeks, effectively ruling him out of the opening two rounds of Munster's Pool 3 campaign. They kick-off their campaign with a clash with London Irish that pits the top teams in the Aviva Premiership and the Magners League against each other.
As well as the game at the Madejski Stadium this weekend, and next week's Round 2 match with Toulon, the 26-year-old is also likely to miss up to three Magners League ties.
O'Leary's injury comes on top of the news this week that centre Liefeimi Mafi has been banned for seven weeks for a dangerous tackle and will make the scrum half a real doubt for Ireland's four Autumn internationals next month.
Munster coach Tony McGahan is also missing skipper Paul O'Connell and Irish hooker Jerry Flannery at present, but is hopeful that British & Irish Lions centre Keith Earls might be fit to return soon.
O'Leary was forced to miss the Lions tour to South Africa in 2009 when he broke his leg in a game against the Scarlets and missed much of last season's Pool campaign. Veteran Irish international Peter Stringer and 24-year-old Duncan Williams are likely to fill in for O'Leary.
