Animal worn on the foot? (4)
I believe the answer is:
mule
I believe this clue is a double definition.
'animal' is the first definition.
(offspring of a donkey and a horse)
'worn on the foot' is the second definition.
(mule is a type of backless shoe)
(Other definitions for mule that I've seen before include "Obstinate quadruped" , "Hybrid beast" , "Proverbially stubborn animal" , "Slipper - beast of burden" , "The animal said to be stubborn" .)