Decline in demand, I predict (3)
I believe the answer is:
dip
'decline' is the definition.
(both can mean to fall or droop)
'in demand i predict' is the wordplay.
'in' indicates a hidden word.
'DIP' is hidden within 'demand i predict'.
(Other definitions for dip that I've seen before include "Thick sauce; brief swim" , "Pickpocket" , "Informally a short bathe" , "Sink; brief swim" , "A brief informal swim" .)