"It is a concern," admitted coach Joe Schmidt.
Clermont can call on Nathan Hines, Canadian Jamie Cudmore and French internationals Julien Pierre and Loic Jacquet as a quartet of second rows to match any squad in Europe.
In contrast, Leinster have been hit with the loss of both Nathan Hines and the short-term signing of Brad Thorn - he has made a commitment to the Otago Highlanders - in consecutive seasons.
"We thought that with Tom Denton and Quinn Roux coming in this year - they are both young men who I think have got futures in the game - that that would alleviate the problem to a degree.
"We've got Dev (Toner), who goes really well for us, and real experience in Damian Browne and obviously our skipper (Leo Cullen).
"But, with Tom getting injured and Brownie having a knock and, then, on top of that, you lose Quinn, you don't have to be a mathematician to work out that five minus three is uncomfortable."
South African Roux has been hit by a shoulder dislocation suffered when he landed heavily from a lineout against Glasgow Warriors on Friday night.
"He is a big, strong man and we were starting to get a bit excited about what he could bring to help us out and he is really gutted," said Schmidt.
"It was just the way he fell and his shoulder dislocation is bad enough and I would say he is probably looking at 16 to 20 weeks rehabilitation."
The explosive nature of Ireland's seven-try demolition of Argentina should have a positive knock-on effect on Leinster's contingent as Zebre come to Dublin in the Pro12 League on Saturday evening.
"It is great to get them back in good head space as well and in a really positive frame of mind and deservedly so," said Schmidt.
Centre Eoin O'Malley could also be in line to make a contribution against the bottom club in the league.
Brian O'Driscoll and Rob Kearney have had mid-January pencilled in as their return-to-play dates, just in time for rounds five and six of the European Cup.
"We will be guided by the surgeons and specialists, who determine what sort of state they are in and as soon as they are back and ready to be fully integrated, we will be delighted to include them again."
Luke Fitzgerald is waiting for medical permission to resume his playing career after what has been a testing six months.
"Luke is in great shape. If you saw him out there training he is very sharp on his feet and it is just about waiting for the all clear so that he can take full contact again.
"That might be one, two or three or four weeks away but I wouldn't expect it to be any more than that, if that. He has made really good progress and he is ahead of schedule.
"We got a bit excited that he might be a bit further ahead than that but unfortunately we have to be a bit patient and we have to be prepared to do so because he is a top-quality member of our environment."