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'm not sure about 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" .)