Is anything changed in the tank?
If nothing seems wrong with him besides eating and croaking less i supose temperature dropped or/and humidity got down?
They tend to be less active during their resting period in nature,
same as the frogs outdoors, they are not at the same activity level year round.
If really nothing changed, try putting the temperature and humidity up and see how he does.
Usually after a good spraying they will be more active for a while.
Hopefully i'm right on this and nothing is wrong with him