I just need a bit more info...

How large is the cricket compared to this toad? and is this one of the two smaller toads? Is his missing hand an open wound or is it healed over? and what temperature is the tank? Also, exactly what type of FBT is he? What type of wood is the tree stump (some woods prove toxic to amphibians)? Is their substrate able to be burrowed into (FBT's will do this, when they feel insucure)?

It's actually best to keep them isolated when you have to monitor feeding. You could try feeding him something that moves slower like butterworms or mealworms, just don't use these as a staple diet once he's recovered. I'll try to answer your questions more clearly, I just need more info. Good luck!!!