Great boxer destined to lose core support (7)
I believe the answer is:
aliment
'support' is the definition.
(thesaurus)
'great boxer destined to lose core' is the wordplay.
I cannot really see how this works, but
'boxer' could be 'ali' (Muhammad Ali) and 'ali' is located in the answer.
The remaining letters 'ment' is a valid word which might be clued in a way I don't understand.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for aliment that I've seen before include "Sustenance" , "Something which nourishes - meal tin (anag)" , "Old word for food" , "Nourishment" .)