German leader has the opportunity to turn up (10)
I believe the answer is:
chancellor
'german leader' is the definition.
(term for the head of the German government)
'the opportunity to turn up' is the wordplay.
'the opportunity' becomes 'chance' ('chance' can be a synonym of 'opportunity').
'to turn' becomes 'roll' (rolling is a kind of turning).
'up' is a reversal indicator (in down clue: letters go upwards).
'roll' reversed gives 'llor'.
'chance'+'llor'='CHANCELLOR'
'has' acts as a link.
(Other definitions for chancellor that I've seen before include "11 17 down [CABINET MINISTER]" , "Head of government" , "chief minister" , "Imposer of taxes" , "Government leader" .)