Johnny Sexton is unlikely to feature for Leinster before Ireland's Six Nations opener at the start of February, according to Leo Cullen.
The out-half damaged knee ligaments during last week’s 43-16 win over Northampton Saints and has been to the UK to see a specialist.
Ireland, under new coach Andy Farrell, begin their Six Nations campaign at home to Scotland on 1 February.
"You would love if he was back [for Leinster], but it’s probably more realistic for Ireland, I think," the head coach said ahead of tomorrow’s Champions Cup clash with the Saints at the Aviva (5.15pm).
"He’s seeing somebody in the UK and he’ll go back there just to get an update in a couple of weeks, but he’s working hard to try and get himself back as quickly as possible, but he won’t be a million miles away hopefully.
"You could see he twisted his knee, and like I said he’s seeing a specialist. He’s under control and on the mend now."
Ross Byrne starts in Sexton's absence, while Scott Fardy steps in to skipper the team.
Leinster are currently top of Pool 1 with 14 points from a possible 15.
Follow all the weekend's Champions Cup action with RTÉ Sport Online and the RTÉ News Now app and listen to live coverage of Leinster v Northampton on RTÉ Radio 1's Saturday Sport.
Cullen on Sexton - 'He's working hard, he's making good progress' - Leinster likely to be without captain until after Six Nations #rterugby https://t.co/xrqgI2X1qk pic.twitter.com/Pt4FItn36s— RTÉ Sport (@RTEsport) December 13, 2019