Setter's knockout numbers performed in Greece (7)
I believe the answer is:
mykonos
'performed in greece' is the definition.
I know nothing about this answer so I can't judge whether it can be defined by this definition.
'setter's knockout numbers' is the wordplay.
'setter's' becomes 'my' (belonging to the crossword setter).
'knockout' becomes 'ko' (abbreviation).
'numbers' becomes 'nos' ('no' is an abbreviation for number).
'my'+'ko'+'nos'='MYKONOS'
Can you help me to learn more?
(Another definition for mykonos that I've seen is " holiday island".)