A model written up for Greek writer (5)
I believe the answer is:
aesop
'greek writer' is the definition.
(I've seen this before)
'a model written up' is the wordplay.
'model' becomes 'pose' ('pose' can be a synonym of 'model'**).
'written up' shows that the letters should be reversed in order.
'pose' written backwards gives 'esop'.
'a'+'esop'='AESOP'
'for' acts as a link.
(Other definitions for aesop that I've seen before include "Great Greek teller of animal fables" , "Greek father of fables" , "Fabulous writer" , "very old writer" , "he wrote in Greek" .)