Requirement after flat tummy somewhat expanded (5,4)
I believe the answer is:
spare tyre
This clue is a double definition.
'requirement after flat' is the first definition.
(after a flat tyre)
'tummy somewhat expanded' is the second definition.
(spare tyre can mean belly fat)
(Other definitions for spare tyre that I've seen before include "Extra fat around the waist" , "Roll of fat around the tummy" , "Extra weight round one's middle" , "Surplus fat on the midriff" , "Part of corporation" .)