Aintree unsettled apprentice (7)
I believe the answer is:
trainee
'apprentice' is the definition.
(I've seen this before)
'aintree unsettled' is the wordplay.
'unsettled' indicates anagramming the letters.
'aintree' with letters rearranged gives 'TRAINEE'.
(Other definitions for trainee that I've seen before include "Person being instructed in work" , "One being taught a job" , "One taking instruction" , "novice" , "As pupil" .)