Johnny Sexton and Jack Conan are due to return to training at some stage next week but are unlikely to feature in Leinster's Champions Cup opener against Bath.
However, the Ireland duo could make their comeback from injuries suffered during the Autumn Series for the trip to Montpelier the following week.
Jamison Gibson-Park could be available for the Bath game after his outstanding Ireland displays last month, having shaken off a quad injury and trained this week.
James Ryan is training with the province but it is unknown as yet when he will return, after it emerged he must see an independent consultant under World Rugby rules after suffering a number of head injuries.
"It's for the welfare of the player and that’s the most important bit, that James is seen by the best people out there," said Blues boss Leo Cullen.
"We will see how that goes off the back of that consultation and we’ll put a proper plan in place off the back of that.”
Meanwhile, Cullen revealed that as of yesterday lunchtime rivals Munster had not been in touch about loaning players for the Champions Cup, given their Covid-caused personnel issues.
The Reds were boosted later by EPCR's announcement that the deadline to register players for the tournament has been extended to Wednesday next.
While Scarlets, who are in a similar position to Munster, have asked Ospreys for players, Cullen said: "It hasn't cropped up, is the honest answer. Nothing has been talked about.
"This year and last year we just register our senior and Academy players, so I don't understand how that would work.
"But, it hasn't been discussed here as of yet."
