Robbie Henshaw has been ruled out of action until January, Leinster have confirmed.
The Ireland centre has had surgery on a wrist injury.
Leo Cullen issued the injury update in the lead up to the province's URC clash with Ulster at the RDS on Saturday.
There was more positive news on Harry Byrne and Rónan Kelleher who have come through the game at the weekend against Glasgow Warriors with no issues after their return from hamstring injuries.
Ryan Baird similarly came through that game following his return from the Graduated Return to Play Protocols.
Jordan Larmour will train fully with the squad this week after his recovery from a foot injury while James Lowe will train fully with the squad this week after his recovery from a calf injury.
Johnny Sexton will be further assessed as the week goes on for a calf injury before a final decision is made on his availability, the club says.
Henshaw will miss this weekend's intrerpro as well as back-to-back Champions Cup games against Racing and Gloucester before the St Stephen's Day showdown with Munster in Limerick.