Missing can inside, but not drinking (9)
I believe the answer is:
abstinent
'not drinking' is the definition.
(I've seen this before)
'missing can inside' is the wordplay.
'missing' becomes 'absent' (similar in meaning).
'can' becomes 'tin' (both are metal containers).
'inside' indicates putting letters inside.
'absent' going around 'tin' is 'ABSTINENT'.
'but' is the link.
(Other definitions for abstinent that I've seen before include "without booze" , "Refusing alcohol" , "Keeping off alcohol" , "Avoiding port, perhaps" , "nowhere near the drink" .)