Aintree fixture for apprentice? (7)
I believe the answer is:
trainee
'apprentice?' is the definition.
(someone undergoing training)
'aintree fixture' is the wordplay.
'fixture' indicates an anagram (fixture historically meant an act of fixing).
'aintree' is an anagram of 'TRAINEE'.
'for' acts as a link.
(Other definitions for trainee that I've seen before include "One taking instruction" , "Person being taught" , "Job learner" , "Person under instruction" , "Student" .)