Man expected to smuggle diamonds (4)
I believe the answer is:
dude
'man' is the definition.
(I know that dude is a type of man)
'expected to smuggle diamonds' is the wordplay.
'expected' becomes 'due' (similar in meaning).
'to smuggle' means one lot of letters goes inside another (smuggle can mean to secretly carry).
'diamonds' becomes 'd' (abbreviation in card games).
'due' going around 'd' is 'DUDE'.
(Other definitions for dude that I've seen before include "He's no cowboy" , "Stylish and confidant man" , "(Cool) chap?" , "admirable man" , "Man (US colloq.)" .)