Work at back of company in small enclosure (4)
I believe the answer is:
coop
'small enclosure' is the definition.
'work at back of company' is the wordplay.
'work' becomes 'op' (abbreviation for opus).
'at back of' means one lot of letters go next to another.
'company' becomes 'co' (abbreviation).
'op' put after 'co' is 'COOP'.
'in' is the link.
(Other definitions for coop that I've seen before include "pound" , "Pen" , "Store" , "box of chickens" , "Birdcage" .)