Will Connors will miss the rest of Leinster's season as the province confirmed that James Ryan and Garry Ringrose will be absent for Saturday's PRO14 final against Munster.
However Luke McGrath will be available after passing the graduated return to play protocols, while Sean Cronin had no reaction having returned from a back injury in Friday's loss to Ospreys.
Connors, the openside who had been in outstanding form, is out for up to eight weeks after suffering a knee injury in training before Ireland's final Six Nations encounter with England last weekend.
Ringrose's ankle injury while on Ireland duty caused him to miss the England game and the province report that he will be unavailable for "a number of weeks", ruling him out of the Champions Cup last 16 tie against Toulon next week.
Ryan could be available for the Toulon game but Leinster have pledged to make sure he is fully fit after suffering two head injuries during the Six Nations. He is currently following graduated return to play protocols.
Cullen said: “He's OK, he was in here during last week. Because it's another head knock, it's important that we take care of these guys.
“We have Caelan who is 22 years of age, James is 24, we want those guys to be around for a long time.
“Everyone just wants to do what's right by them.
"We will explore the best people that are out there, just to make sure there is a proper plan in terms of their safe return to rugby, whenever that is.
“It's a bit week-by-week at the moment. I don't have anything concrete to give you.
“James came around very, very quickly (against Scotland). He cops an elbow from Hamish Watson in a tackle near the end of the game. You see he has a stumble there, but talking to him, he knew exactly what was going on at the time.
“But we still need to find out... it's not his first head knock this season, so we will find out exactly what's going on with him there and make sure that he is taken care of.
“The welfare of the players is key. We'll try and do what's best by the fellahs.”
Young scrum-half Rowan Osborne picked up a hand fracture in the Ospreys defeat and will undergo surgery this week, though Jamison Gibson-Park is among the host of frontliners who will return to Leo Cullen's squad today.
