About to have nothing but deer (3)
I believe the answer is:
roe
'deer' is the definition.
(roe deer is a kind of deer)
'about to have nothing' is the wordplay.
'about' becomes 're' ('re' means regarding or about).
'to have' means one lot of letters goes inside another.
'nothing' becomes 'O' (looks like zero - 0).
're' placed around 'o' is 'ROE'.
'but' is the link.
(Other definitions for roe that I've seen before include "A mass of fish-eggs" , "eg Caviare" , "Fish eggs; small deer" , "Food from fish" , "Part of fish, sounds like go through water" .)