Leinster out-half Ross Byrne has been ruled out of action until the New Year with an arm injury.
The 28-year-old suffered the injury early in the province's BKT URC victory over Munster on 25 November.
"Ross Byrne had a procedure on an arm injury last week and will be unavailable until the New Year," said the club.
Utility back Jamie Osborne, who started on the wing for Saturday's win over Connacht, has also been ruled out for a spell.
The province said the 22-year-old "picked up a shoulder injury in the win over Connacht and is having a procedure this week and will be unavailable for selection as a result."
"I think that's just part of the game unfortunately," Leinster head coach Leo Cullen said.
"It's a blow for him, but he'll come back strong. It's an opportunity for someone else, and that's the way we have it, the next man up mentality We're lucky with the group we have, there's lots of guys itching to get their opportunity once someone drops."
The province will have Harry Byrne, Ciarán Frawley and Sam Prendergast fighting it out for the out-half shirt for Sunday's Investec Champions Cup opener away to La Rochelle.
But Cullen was non-committal over who will get the 10 shirt for the coming weeks.
"We're contemplating at the moment," he added, with a wry smile.
"It's a great challenge for us this week, so whoever gets to wear the 10 jersey, or any jersey from 1 to 23.
"It's a magical place to go, France, to play in this competition. There's no tougher place to go than the defending champions, and it's a great test of the group. It's what you want, to test yourself against the best."
There was some good news, however, after scrum-half Cormac Foley and prop Cian Healy both came through the Connacht match unscathed having recovered from recent shoulder injuries.
Back row Alex Soroka has recovered from a foot injury and has resumed training, while prop Michael Milne (shoulder) will be assessed later this week.
There were no further updates on Tommy O’Brien (ankle), Luke McGrath (knee) and John McKee (hamstring).
Watch Munster v Bayonne in the Champions Cup on Saturday from 4.45pm on RTÉ2 and RTÉ Player, follow a live blog on www.rte.ie/sport and the RTÉ News app or listen to commentary on RTÉ Radio 1
