Bank manager the real McCoy, ultimately (4)
I believe the answer is:
rely
'bank' is the definition.
(to bank on something is to rely on it)
'manager the real mccoy ultimately' is the wordplay.
'ultimately' indicates one should take the final letters.
The final letters of 'manager the real mccoy' are 'RELY'.
(Other definitions for rely that I've seen before include "Depend, bank" , "Have confidence or faith in" , "Count" , "Bank (on someone)" , "Run and see" .)