Dog followed, diminished (9)
I believe the answer is:
curtailed
'diminished' is the definition.
(thesaurus)
'dog followed' is the wordplay.
'dog' becomes 'cur' (both can mean a despicable person).
'followed' becomes 'tailed' (I've seen this before).
'cur'+'tailed'='CURTAILED'
(Other definitions for curtailed that I've seen before include "Cut short" , "Broken off" , "Made short" , "Clipped" , "Reduced" .)