Robbie Henshaw has emerged as a major doubt for Leinster's Heineken Champions Cup quarter-final against Ulster on Saturday week.
Henshaw has yet to recover from the dead leg that he sustained ahead of Ireland' Six Nations win over Scotland and is not in a position to return to on-field training.
The reigning European champions host Ulster at the Aviva Stadium on Saturday, 30 March and assistant coach Stuart Lancaster has confirmed that he is facing a race to be fit for the game.
"Very frustrating for Robbie, I feel sorry for him," Lancaster is quoted as saying in the Irish Independent.
"He's had two different injuries that have had different lengths out and he's so frustrated himself. We'll see, he's not on field with us yet so obviously the clock is ticking towards Ulster.
"We'll have a better idea come Monday/Tuesday next week but again you get to the point in a week where you can't wait. He's making progress, he's not far off but as to make he'll Ulster we'll see."
Josh van der Flier sustained a groin injury while with the national team and he is set to undergo a scan to determine how long he will be sidelined for.
"He's gone for a scan today and seeing the specialist tomorrow so we'll find out a bit more," Lancaster explained.
"I don't think he'll be available for the next week or two, but as to how many weeks, it'll depend on tomorrow."
Devin Toner, meanwhile, remains sidelined with the ankle injury he sustained during Ireland's loss to England at the start of February.
While he is ahead of schedule in his recover, the second row will not be ready to face Ulster.
There was better news regarding Dan Leavy, Luke McGrath, Joe Tomane and Nick McCarthy as they are all available for Friday's Guinness PRO14 clash with Edinburgh.
Leinster's Heineken Champions Cup quarter-final against Ulster on Saturday, 30 March is live on BT Sport on the eir sport pack [kick-off 5.45pm]. Subscribe here
Image: Inpho Photography