Initially ready to please, suffering setback (7)
I believe the answer is:
relapse
'setback' is the definition.
(I've seen this in another clue)
'initially ready to please suffering' is the wordplay.
'initially' indicates taking the first letters.
'to' means one lot of letters go next to another.
'suffering' indicates anagramming the letters.
The first letter of 'ready' is 'r'.
'please' with letters rearranged gives 'elapse'.
'r'+'elapse'='RELAPSE'
(Other definitions for relapse that I've seen before include "Fall back into bad health" , "Get worse again" , "A return to illness" , "Become ill again" , "Become sick again" .)