Centre Wallace left the field with a migraine during Friday's RaboDirect Pro12 defeat to Leinster, while former South Africa back-rower Wannenburg sustained a groin problem.
Wallace's migraine improved shortly after the conclusion of the match, while Wannenburg's injury is responding well to treatment. But number eight Henry is battling to be fit as he tries to recover from an ankle sprain and scrum-half Marshall has an elbow problem.
An Ulster statement read: "Chris Henry sustained an ankle sprain which is subject to ongoing treatment and re-assessment but at this stage he is not ruled out of contention.
"Paul Marshall continues to receive treatment for the injury to his right elbow sustained in the match against Connacht and re-assessment is ongoing."