Oliver is having one portion? Must be feeling queasy (8)
I believe the answer is:
liverish
'feeling queasy' is the definition.
'oliver is having one portion?' is the wordplay.
'one portion?' says the answer is hidden in the clue (I've seen 'portion of' mean this).
'LIVERISH' can be found hidden inside 'oliver is having'.
'must be' acts as a link.
(Other definitions for liverish that I've seen before include "slightly ill" , "Crotchety" , "a bit off?" , "Irritable as from bodily disorder" , "Like foie gras" .)