Fake medic turned away (3)
I believe the answer is:
cod
'fake' is the definition.
(cod can mean false or inauthentic)
'medic turned away' is the wordplay.
'medic' becomes 'doc' (doctor).
'turned away' shows that the letters should be reversed in order.
'doc' reversed gives 'COD'.
(Other definitions for cod that I've seen before include "Pay when you get the goods - sounds fishy" , "faked" , "Large sea fish- it's a sham" , "A foolish sort of a fish" , "mock" .)