Singer is withdrawn from this race (6)
I believe the answer is:
thrush
'singer' is the definition.
(type of songbird)
'is withdrawn from this race' is the wordplay.
'withdrawn from' suggests deleting specific letters.
'race' becomes 'rush' (synonyms).
'this' with 'is' taken out is 'th'.
'th'+'rush'='THRUSH'
(Other definitions for thrush that I've seen before include "Mouth fungus or songbird" , "Singing bird or mouth-troat infection" , "Song bird" , "Songster" , "Songbird with brownish back and speckled breast" .)