He's not in favour of work with a model (7)
I believe the answer is:
opposer
'he's not in favour' is the definition.
The definition suggests a singular noun which matches the answer.
'work with a model' is the wordplay.
'work' becomes 'op' (abbreviation for opus).
'with' says to put letters next to each other.
'a model' becomes 'poser' ('poser' can be a synonym of 'model').
'op'+'poser'='OPPOSER'
'of' acts as a link.
Can you help me to learn more?
(Other definitions for opposer that I've seen before include "Second speaker in debate" , "One offering resistance" , "The one against the motion" , "Person against the motion" , "Adversary" .)