Fighter’s time in celebrity group (1-4)
I believe the answer is:
'celebrity group' is the definition.
(A-list can mean very famous people)
'fighter's time' is the wordplay.
'fighter's' becomes 'Ali's' (boxer Muhammad Ali).
'time' becomes 't' (abbreviation).
'in' acts as a link.
(Other definitions for a-list that I've seen before include "Most celebrated people" , "Very famous" , "of the best sort" , "Top celebrity group" , "Acclaimed" .)