Tadhg Furlong's return to competitive action has been delayed after he failed to progress as expected in his recovery from a calf injury.
The Ireland international has yet to feature for Leinster since rugby's return in August due to a combination of back and calf problems.
He looked to be closing in on a return after Leinster reported that he had stepped up his training earlier this month, but his progress has been slow and he will not be available for this week's Guinness PRO14 clash against Cardiff at the RDS.
Head coach Leo Cullen has also confirmed that Ciaran Parker will be sidelined for a number of weeks after undergoing a procedure on the thumb injury he picked up in Monday's defeat of Edinburgh
On a more positive note, Sean Cronin (thumn) and Rory O'Loughlin (shoulder) will train with the team this week, while Ryan Baird came through his first game back from an adductor injury without any issues and is available for selection.
See five LIVE Guinness PRO14 games this weekend, including Leinster v Cardiff (eir sport 1, Sun, Nov 22, 5.15pm)