However, the management are optimistic that the Ireland back rower will be available for selection ahead of Friday's team announcement.
Isaac Boss (tight hamstring) was a late withdrawal from the panel, but the medical team are hopeful that he too will be available having made his 50th Heineken Cup career appearance in the round 2 victory over Castres Olympique.
Cian Healy has a leg injury which will continue to be assessed by the medical team, but he is still in contention for next weekend.
Speaking at a media briefing today, Leinster skills & kicking coach Richie Murphy said: "Sean O'Brien came off with a dead leg at the weekend but he should be fine. Dave Kearney will be fine.
"Cian had a scan on his ankle this morning. The results aren't known yet so we're waiting to hear. He's a doubt for the weekend...he picked up a knock in training.
"It was one of these things that just happen, there was nothing to it. But he went over on his ankle. We just have to wait and see how bad it is."
Sean Cronin's next game will be his 60th in Leinster colours, Rhys Ruddock is one game away from the-70 cap milestone, while prop Jack McGrath is now two caps shy of the half century mark in all competitions for Leinster.
Out-half Ian Madigan's 10-point haul in Northampton took him to the 400-point career landmark in his 89 games to date.
The Leinster 'A' team kept up their winning run on Saturday with a 31-0 victory over Cross Keys at Donnybrook. There are no major injury concerns for Girvan Dempsey's men ahead of their return fixture at Pandy Park next Saturday afternoon (kick-off 3pm).
Leinster Rugby is proud to support the great work of the Irish Youth Foundation and Arc Cancer Support Centre. This Saturday there will be an envelope on every seat at the Aviva Stadium.
Please help us to help them by putting €2 or what you can into your envelope and pop it into the Santa sacks located around the stadium at half-time or after the match. There are some amazing prizes on offer including a chance to be coached by members of the Leinster squad.
Tickets sales for Saturday's game have now passed the 41,500 mark. Tickets are on sale online here and from the Leinster Rugby Store (Donnybrook), Spar (Donnybrook), Active Sports (Blackrock) as well as Ticketmaster outlets nationwide. Tickets are available from €20.