Advance of French victor overturning European (7)
I believe the answer is:
develop
'advance' is the definition.
(I know that advance is a kind of develop)
'of french victor overturning european' is the wordplay.
'of french' becomes 'de' ('of' in French).
'victor' becomes 'V' (phonetic alphabet: alpha, bravo, charlie etc.).
'overturning' is a reversal indicator.
'european' becomes 'pole' (someone from Poland).
'pole' in reverse letter order is 'elop'.
'de'+'v'+'elop'='DEVELOP'
(Other definitions for develop that I've seen before include "Grow, progress" , "Unfold" , "'Grow, evolve (7)'" , "Grow, elaborate" , "issue" .)