Ulster second-row, Dan Tuohy, was injured in Ulster’s 9 points to 10 defeat to Northampton Saints at Ravenhill on Saturday night.
A scan Monday afternoon revealed that he has a torn calf muscle and that he will be out for up to four weeks.
Paddy Jackson sustained a dead leg in the same match. He is responding well to treatment and will likely be available for selection for the RaboDirect PRO12 game against Leinster on Friday evening.
No date has yet been set for Tommy Bowe's knee surgery but it is expected that it will take place before the end of this week.