Slow mover tires too, unfortunately (8)
I believe the answer is:
tortoise
'slow mover' is the definition.
(I've seen this before)
'tires too unfortunately' is the wordplay.
'unfortunately' indicates an anagram.
'tires'+'too'='tirestoo'
'tirestoo' is an anagram of 'TORTOISE'.
(Other definitions for tortoise that I've seen before include "Shelled animal" , "Slow-moving land reptile" , "Expected to be slow" , "One shelled" , "Slow-moving reptile that won race against a hare" .)