The Leinster quartet of Robbie Henshaw, Tadhg Furlong, Jimmy O’Brien and Tommy O'Brien all have question marks over their fitness just over two weeks out from the start of the Six Nations.
With Andy Farrell due to name his Six Nations squad on Wednesday the hope is that all four will be included but an injury update from Leinster after their Champions Cup victory away to Bayonne will be of some concern.
Jimmy O'Brien picked up a hamstring injury in that game, Henshaw a knee injury while Furlong and Tommy O'Brien both suffered calf injuries.
Ireland centre Henshaw suffered a knee injury in the 34th minute, while wing Tommy O'Brien pulled up with a calf injury just after the break.
Full-back Jimmy O'Brien was taken off near the end due to injury and at the time Cullen said he believed they were mostly soft-tissue injuries.
All four will be assessed later in the week by Leinster ahead of their URC clash with Connacht at Dexcom Stadium on Saturday.
"We'll take the lead there from the medical team," senior coach Jacques Nienaber told RTÉ Sport when asked how hopeful he is about their availabilty for Saturday's URC game against Connacht.
"A lot of guys went for scans today so we will wait and see what the outcome is of that. Up to now there is no clarity so I'd just be speculating on them.
"We'll wait and see tomorrow morning when the results come back."
There is better news elsewhere however as both Ciarán Frawley and Jack Conan are available for the trip to Galway, while both Hugo Keenan (hip) and Jamie Osborne (shoulder) continue their recovery from serious injuries.
Connacht tighthead prop Finlay Bealham is currently injured and alongside Leinster and Ireland loosehead prop Andrew Porter, who can cover tighthead, is expected to miss the opening round of the Six Nations against France on 5 February.
Paddy McCarthy, who dovetailed with Porter in the November internationals, is also sidelined with a foot issue.
