Right - improve, please, or 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' (common abbreviation).
'improve' indicates an anagram.
'please' anagrammed gives 'elapse'.
'r'+'elapse'='RELAPSE'
'or' acts as a link.
(Other definitions for relapse that I've seen before include "go back" , "Return to sickness" , "Slip back to former state" , "Fail to maintain progress" , "Deterioration after period of improvement" .)