Car has lost ability to accelerate,5 speed manual. Can it be the clutch slipping

could be, does the engine rev high even though it' low speed? If so yes the clutch is finished, if not then the next likely thing could very well be catylitic converter is plugged, a typical symptom of a plugged cat. is an inability to accelerate relly bad gas milage and stillruns good at low speed but not under load, hope this helps