Possibly left Man Utd? (4)
I believe the answer is:
side
'possibly left' is the definition.
The answer and definition can be both man-made objects as well as being singular nouns.
Perhaps you can see a link between them that I don't see?
'man utd?' is the wordplay.
'man' becomes 'Si'.
'utd?' becomes 'de' (I can't justify this - if you can you should believe this answer much more).
'si'+'de'='SIDE'
Can you help me to learn more?
(Other definitions for side that I've seen before include "Pretentious air" , "Team - border" , "Ides (anag.)" , "Manchester United, for example?" , "Lateral team" .)