Thinks highly of one who's always in the reserves? (7)
I believe the answer is:
reveres
'thinks highly of' is the definition.
(revering is a kind of thinking highly of)
'always in the reserves?' is the wordplay.
'always' becomes 'ever' (synonyms).
'in' is an insertion indicator.
'the reserves?' becomes 'res' (I can't explain this - if you can you should give a lot more credence to this answer).
'ever' inserted into 'res' is 'REVERES'.
'one who's' acts as a link.
This may not be correct. Some or all of it may be part of another bit of the clue.
Can you help me to learn more?
(Other definitions for reveres that I've seen before include "Hero-worships" , "Venerates" .)