Love upset animal (4)
I believe the answer is:
vole
'animal' is the definition.
(thesaurus)
'love upset' is the wordplay.
'upset' is an anagram indicator.
'love' is an anagram of 'VOLE'.
(Other definitions for vole that I've seen before include "Small mammal - one to love" , "River-bank rodent" , "River bank rodent" , "win all the tricks" , "Small mouse-like rodent" .)