Small mammal tick gets treated always (5,4)
I believe the answer is:
mouse deer
'small mammal' is the definition.
(I've seen this before)
'tick gets treated always' is the wordplay.
'tick' becomes 'mo' (both can mean a very short amount of time).
'gets' is a charade indicator (letters next to each other).
'treated' becomes 'used' (using is a kind of treating).
'always' becomes 'eer' (poetic way of saying ever).
'mo'+'used'+'eer'='MOUSE-DEER'
(Other definitions for mouse deer that I've seen before include "Small tusked mammal" , "Its beastly" , "Emeer's duo (anag) -- tiny hornless ruminant" , "chevrotain" .)