Right - improve, please, then deteriorate (7)
I believe the answer is:
relapse
'deteriorate' is the definition.
(as in a relapse of a medical condition)
'right improve please' is the wordplay.
'right' becomes 'r' (abbreviation).
'improve' is an anagram indicator.
'please' is an anagram of 'elapse'.
'r'+'elapse'='RELAPSE'
'then' is the link.
(Other definitions for relapse that I've seen before include "Return to sickness" , "Decline" , "Fall back into sickness" , "medical problem" , "Fall back into bad health" .)