Ulster are facing significant injury concerns before their upcoming Challenge Cup match against Zebre in Parma on Saturday.
The squad has lost Eli Snyman, who started at lock alongside Donnell during the previous fixture, to a confirmed concussion.
Three additional players have been identified as doubtful for the trip to Italy: Prop Eduardo Bell, second row Ben Donnell, and full-back Ethan McIlroy.
Bell may not feature after sustaining a hamstring injury during training sessions, having previously seen no playing time in Saturday's United Rugby Championship draw with Munster.
Donnell and McIlroy both picked up unspecified knocks following the same match against Munster, while hooker Tom Stewart also sustained an unidentified knock.
On a brighter note, full-back Michael Lowry has rejoined full team training after recovering from a concussion suffered in the opening URC defeat to Edinburgh on 25 September.
The Reds are currently seeking their first win of the campaign after recording one defeat and two draws in the United Rugby Championship.
Following this fixture in Parma, Ulster will travel to South Africa to face the Bulls and Stormers in upcoming league fixtures.
BBC Sport Northern Ireland reported that four players have emerged as doubts for the Challenge Cup opener against Zebre in Parma on Saturday.