Just one cup can cause physical deterioration (7)
I believe the answer is:
atrophy
'physical deterioration' is the definition.
'atrophy' can be an answer for 'deterioration' (thesaurus). I am unsure of the 'physical' bit.
'just one cup' is the wordplay.
'just one' becomes 'a' (a thing is one thing. I am not sure about the 'just' bit.).
'cup' becomes 'trophy' (I've seen this before).
'a'+'trophy'='ATROPHY'
'can cause' acts as a link.
Can you help me to learn more?
(Other definitions for atrophy that I've seen before include "wasting away" , "Degenerate" , "Decline" , "Waste away (from disuse?)" , "Degeneration" .)