Covid outbreak really frazzled unprepared leaders of Greek island... (5)
I believe the answer is:
corfu
'greek island' is the definition.
(Corfu is a Greek island)
'covid outbreak really frazzled unprepared leaders' is the wordplay.
'leaders' indicates taking the first letters.
The initial letters of 'covid outbreak really frazzled unprepared' is 'CORFU'.
'of' acts as a link.
(Other definitions for corfu that I've seen before include "Ionian holiday island" , "part of Greece" , "holiday destination?" , "Greek island, a British protectorate in C 19" , "One of the Ionian islands" .)