Ireland and Leinster centre Robbie Henshaw will be out of action until January after having wrist surgery.
Leinster coach Leo Cullen said on Monday that Henshaw, 29, “underwent a procedure” last week.
Henshaw will miss the opening rounds of the European Champions Cup and three interprovincial derbies in the United Rugby Championship.
Johnny Sexton is a doubt for Leinster’s game against Ulster on Saturday because of a calf injury.
Sexton, 37, sustained the injury in the warm-up before Ireland’s final autumn international against Australia on 19 November and was a late withdrawal from that game.
Henshaw’s involvement in Ireland’s autumn games was confined to the opening five minutes of the win over Fiji on 12 November, when he had to be replaced because of a hamstring injury.
The former Connacht player’s absence opened the door to Ulster’s Stuart McCloskey, who started all three November games for Andy Farrell’s Ireland side.
Former All Blacks centre Charlie Ngatai is also a doubt for Leinster’s Ulster game at the RDS after sustaining a shoulder injury in Saturday’s win over Glasgow.
Ireland backs James Lowe and Jordan Larmour could be in contention to feature this weekend after returning to Leinster training.
Both missed Ireland’s autumn campaign with wing Lowe not having played this season because of a calf injury and Larmour out since early October because of a foot problem.