Poor ailing animal (6)
I believe the answer is:
nilgai
'animal' is the definition.
(I've seen this before)
'poor ailing' is the wordplay.
'poor' indicates an anagram.
'ailing' with letters rearranged gives 'NILGAI'.
(Other definitions for nilgai that I've seen before include "animal" , "Large Indian antelope, ailing (anag.)" , "creature" .)