Healthy, inspiring new boxer's one who may win (8)
I believe the answer is:
finalist
'one who may win' is the definition.
'healthy inspiring new boxer's' is the wordplay.
'healthy' becomes 'fit' (synonyms).
'inspiring' indicates putting letters inside.
'new' becomes 'n'.
'boxer's' becomes 'alis' (Muhammad Ali).
'n'+'alis'='nalis'
'fit' going around 'nalis' is 'FINALIST'.
(Other definitions for finalist that I've seen before include "He qualified" , "One has reached the last round" , "One at decisive stage" , "Winner of semi-final" , "Competitor who has beaten all except one" .)