Since Stephen returned from France, the injury has flared up once more and even with careful management, he has been unable to both train and play with his province.
While the timing is unfortunate for Ulster, who are making final preparations for tomorrow's first Heineken Cup pool game against Gloucester at Ravenhill, the Ulster Rugby medical staff have this week decided that in the player's long term interest, Stephen must be rested for a period of 4-6 weeks to allow his injury to settle.
Ferris will miss both the opening game in the tournament tomorrow night and next week's trip to Bourgoin, however could be back in contention by round 3 or 4 when Ulster face the Ospreys in back-to-back fixtures.
With back-row forward Neil McMillan already on the injury list, Ferris' unavailability is a blow, however, Kieron Dawson's leg injury sustained against Glasgow last Friday is not as serious as initially thought and the flanker is expected to be named in Mark McCall's squad for Friday's all-ticket game at Ravenhill.