Be apathetic as doctor needing exercise (4)
I believe the answer is:
mope
'be apathetic' is the definition.
(I've seen this before)
'doctor needing exercise' is the wordplay.
'doctor' becomes 'mo' (medical officer).
'needing' is a charade indicator (letters next to each other).
'exercise' becomes 'pe' (Physical Education).
'mo'+'pe'='MOPE'
'as' acts as a link.
(Other definitions for mope that I've seen before include "Become gloomy" , "Go gloomily about" , "Move listlessly and aimlessly" , "Be listless or depressed" , "Poem (anag.)" .)