He's not paid to take a companion to the old city (7)
I believe the answer is:
amateur
'he's not paid to' is the definition.
The answer is a person as well as being a singular noun. This is suggested by the definition.
'a companion to the old city' is the wordplay.
'companion' becomes 'mate' (both can mean a friend).
'to the old city' becomes 'ur' (ancient Sumerian city state).
'a'+'mate'+'ur'='AMATEUR'
'take' acts as a link.
Can you help me to learn more?
(Other definitions for amateur that I've seen before include "refusing payment" , "One is not professional" , "Tum area (anag.)" , "Non-pro" , "Not pro" .)