Not just Macron's a moderate (6)
I believe the answer is:
unfair
'not just' is the definition.
('unfair' is the opposite to 'just')
'macron's a moderate' is the wordplay.
'macron's a' becomes 'un' (French indefinite article 'a' or 'an').
'moderate' becomes 'fair' (similar in meaning).
'un'+'fair'='UNFAIR'
(Other definitions for unfair that I've seen before include "Biassed; not reasonable" , "Partisan" , "raining perhaps?" , "Not equitable-or blonde?" , "Unjust, partial" .)