A little sad, Everyman's a rejected novelist (4)
I believe the answer is:
amis
'novelist' is the definition.
(Kingsley or Martin Amis)
'a little sad everyman's a rejected' is the wordplay.
'little' indicates taking the first letters.
'everyman's' becomes 'I'm' (where the setter is Everyman).
'a rejected' is a reversal indicator.
The first letter of 'sad' is 's'.
's'+'im'='sim'
'sim' backwards is 'mis'.
'a'+'mis'='AMIS'
(Other definitions for amis that I've seen before include "English writer" , "Kingsley -, English author (Lucky Jim)" , "Author of Lucky Jim, d.1995" , "Author Kingsley or Martin" , "Martin --, Eng. author" .)