Inert fellow is in bed after working for a specialist (10)
I believe the answer is:
oncologist
'for a specialist' is the definition.
(oncologist is a kind of specialist)
'inert fellow is in bed after working' is the wordplay.
I cannot really understand how this works, but
'fellow' could be 'co' (eg a co-worker is a fellow worker) and 'co' is found within the answer.
'is' is found in the answer.
'working' could be 'on' (on can mean working or activated) and 'on' is located in the answer.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for oncologist that I've seen before include "Tumour specialist" , "One studying tumours" , "One who studies and treats tumours" .)