Doctor of French left a poser (5)
I believe the answer is:
model
'a poser' is the definition.
('model' can be a synonym of 'poser')
'doctor of french left' is the wordplay.
'doctor' becomes 'mo' (medical officer).
'of french' becomes 'de'.
'left' becomes 'l' (common abbreviation).
'mo'+'de'+'l'='MODEL'
(Other definitions for model that I've seen before include "She saunters on the catwalk" , "She exhibits clothes on the catwalk" , "Representative example" , "She walks the catwalk" , "She parades on the catwalk" .)