About to have nothing but small deer (3)
I believe the answer is:
roe
'small deer' is the definition.
(I've seen this before)
'about to have nothing' is the wordplay.
'about' becomes 're' ('re' means regarding or about).
'to have' indicates putting letters inside.
'nothing' becomes 'o' (O resembles 0).
're' enclosing 'o' is 'ROE'.
'but' acts as a link.
(Other definitions for roe that I've seen before include "Fish eggs; small deer" , "Hoofed animal(s)" , "Mass of fish's eggs" , "Mass of fish eggs" , "A mass of fish-eggs" .)