Leinster hooker Richardt Strauss has been ruled out for four weeks after picking up a knee injury against Clermont in the Heineken Cup.
On Sunday afternoon Strauss underwent a scan on a medial ligament injury he picked up in the opening moments of the game and is expected to be out for approximately 4 weeks.
Flanker Shane Jennings damaged his shoulder against Clermont and was replaced by Jordi Murphy in the final quarter.
Jennings will be monitored by the medical team and is considered a doubt for Friday's game alongside Isa Nacewa who suffered deep bruising to his arm.
Friday's game with Ulster could come a week or two too soon for Luke Fitzgerald, who has stepped up his rehabilitation programme this week, but it is hoped that the Ireland international could come into the frame for either the home game against Connacht or for the Edinburgh match away at Murrayfield the following week.
There was good news for the province with Eoin O'Malley successfully coming through his first outing in the province's 44-13 British & Irish Cup win over Jersey on Sunday afternoon and the centre will potentially come into the frame this week.