A cup showing degeneration (7)
I believe the answer is:
atrophy
'degeneration' is the definition.
(thesaurus)
'a cup' is the wordplay.
'cup' becomes 'trophy' (I've seen this before).
'a'+'trophy'='ATROPHY'
'showing' acts as a link.
(Other definitions for atrophy that I've seen before include "shrivel" , "Waste away, wither" , "Decline" , "Waste away - sounds like a sporting award" , "Waste away through under-nourishment or lack of use" .)