Doctor tries further examination (5)
I believe the answer is:
resit
'further examination' is the definition.
(I've seen this before)
'doctor tries' is the wordplay.
'doctor' indicates an anagram.
'tries' is an anagram of 'RESIT'.
(Other definitions for resit that I've seen before include "Enquiring intrusively (into person's affairs)" , "later exam" , "tested again" , "Exam taken again" , "take another exam" .)