Stammering man's just what's needed by worker (8)
I believe the answer is:
hesitant
'stammering' is the definition.
(thesaurus)
'man's just what's needed by worker' is the wordplay.
'man's' becomes 'hes' (he refers to a man).
'just what's needed' becomes 'it' (as in 'that's it!').
'by' is a charade indicator (letters next to each other).
'worker' becomes 'ant' (worker is a type of ant).
'hes'+'it'+'ant'='HESITANT'
(Other definitions for hesitant that I've seen before include "Undecided, halting" , "Slow to speak or act" , "Demurring" , "The Saint? (anag)" , "Reluctant, feeling indecision" .)