Possibly shrink shirt egghead Pat's worn (9)
I believe the answer is:
therapist
'possibly shrink' is the definition.
(informal term for a therapist or psychiatrist)
'shirt egghead pat's worn' is the wordplay.
'egghead' becomes 'e' (head letter of 'egg').
'worn' is an anagram indicator (worn can mean damaged).
'shirt'+'e'+'pat'='shirtepat'
'shirtepat' with letters rearranged gives 'THERAPIST'.
(Other definitions for therapist that I've seen before include "One giving treatment" , "One who treats or heals" , "Provider of relieving 57 Across" , "Curative healer" , "Medical practitioner" .)