Jim Mallinder says George North should be fit to face Ospreys next Sunday after the Wales wing went off with a jaw injury at Castres.
North was withdrawn with 10 minutes to go, with Kiwi utility back James Wilson thrust into the action.
Saints lost the game 19-13 as Castres claimed a crucial victory in the Heineken Cup Pool 1 opener at Stade Pierre-Antoine.
Northampton’s attentions now turn to Sunday’s showdown with Ospreys at the Gardens, and North looks set to be fine for that clash.
“He got a bang to his jaw so he’s just a bit sore,” said director of rugby Mallinder.
“I don’t think he’s broken anything so he should be fine for next week.”