Deteriorate as leper unfortunately (7)
I believe the answer is:
relapse
'deteriorate' is the definition.
(I've seen this before)
'as leper unfortunately' is the wordplay.
'unfortunately' indicates anagramming the letters.
'as'+'leper'='asleper'
'asleper' with letters rearranged gives 'RELAPSE'.
(Other definitions for relapse that I've seen before include "Fall back into former condition, being pleaser" , "Deterioration in health" , "Fall back into former state" , "Get into bad habits again" , "fall into sin" .)