This man's with it — worker maybe destined to lose? (8)
I believe the answer is:
Here is my best explanation:
'maybe destined to lose?' is the definition.
(reference to the phrase 'he who hesitates is lost')
'this man's with it worker' is the wordplay.
'this man's' becomes 'hes' (he's).
'with' is a charade indicator (letters next to each other).
'worker' becomes 'ant' (worker is a type of ant).