There is something of a make-or-break significance to this one.
The French club is up and running with maximum points pocketed from their two rounds to head Pool Five.
In contrast, Ulster Director of Rugby Les Kiss must be reaching a point of frustration based on the inconsistent form that has them located fifth in the PRO12 and third in the Pool.
This was never better illustrated this season than in the way they lurched from commanding for most of the first-half at Bordeaux to crippling in the second.
If Ulster switch off for one minute against Clermont, they will be toasted by a powerful unit which dismantled the normally resilient Exeter at Sandy Park.
They do not suffer from the travel bug which often infects French clubs in Europe.
This will have to be one of those unforgettable afternoons in Ravenhill or Ulster will be in dire trouble.