The Springbok winger cracked a bone in his foot after colliding with team-mate Adrian Durston at training, and was forced to sit out the crushing 39-3 win over the Cardiff Blues last weekend.
Ospreys manager Derwyn Jones said was expected to back running well before the Castres clash on October 23.
''We're hoping he'll be back sooner,'' he said. ''We'll see what the doctors say but it would be nice if he could return a week or two before Europe so he can get back into it.''
The Ospreys have several options out wide, with the likes of Aled Brew, Dave Tiueti and Paul Mackey in the frame to replace Terblanche