Zac Ward sustained a concussion playing for the Ulster 'A' team against Connacht Eagles last Friday.
He will now follow the World Rugby Graduated Return to play protocols and is unavailable for selection this week.
Ben Moxham (hamstring) was injured in the same game and his fitness for selection will be monitored during training ahead of the fixture against Leinster this Friday.
Other players currently unavailable for selection are: Robert Baloucoune (calf), Jake Flannery (ankle), James Hume (knee), Callum Reid (knee), Ethan McIlroy (ankle), Sean Reffell (ankle), Jacob Stockdale (hamstring).
Tom Stewart (ankle) and Stewart Moore (sterno-clavicular joint) have both reintegrated into full team training following their recent injuries and are available for selection.
Nick Timoney has been released from Ireland duty and is also available for selection.