Hesitate to leave sick inside (9)
I believe the answer is:
vacillate
'hesitate' is the definition.
(vacillating is a kind of hesitating)
'leave sick inside' is the wordplay.
'leave' becomes 'vacate' (to vacate a place is to leave it).
'sick' becomes 'ill' (synonyms).
'inside' is an insertion indicator.
'vacate' going around 'ill' is 'VACILLATE'.
'to' acts as a link.
(Other definitions for vacillate that I've seen before include "Dither" , "Sway to and fro" , "Be unsteady" , "Be irresolute" , "Keep changing one's mind" .)