Aesop's also-ran (4)
I believe the answer is:
hare
'aesop's also-ran' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for hare that I've seen before include "Leveret" , "'First catch your ....; then cook it'" , "Timid creature" , "Sort of rabbit" , "Old saying: 'Let the .... sit" .)