Fergus McFadden will miss the next six weeks of his last season for Leinster while Conor O'Brien is out for the rest of the season.
McFadden, 34, signed a short term deal to play for the province until the end of the campaign but won't get a chance to play again unless Leinster make the last four of the Champions Cup.
The utility back three veteran picked up a calf injury in training and, according to Leinster head coach Leo Cullen, will be out for six weeks.
O'Brien, meanwhile, had a procedure last week on a long-standing hamstring problem and is expected to be unavailable for a number of months.
The news will come for a blow Cullen, who is preparing for the restart of the Guinness PRO14 championship, with Leinster to face Munster on Saturday in the Aviva Stadium.
Dan Leavy will go up another gear towards full training this week and won't be involved in the opening game back.
Peter Dooley is to return to training this week after a shoulder injury, but Vakh Abdaladze is due to have a procedure this week on a long-standing back issue.
