Giant bikes require work to replace a bearing (7)
I believe the answer is:
cyclops
'giant' is the definition.
(one-eyed giant in Greek myth)
'bikes require work to replace a bearing' is the wordplay.
I cannot quite understand how this works, but
'work' could be 'op' (common abbreviation for 'opus') and 'op' is found within the answer.
'bearing' could be 's' and 's' is present in the answer.
This may be the basis of clue (or it may be nonsense).
(Other definitions for cyclops that I've seen before include "antagonist of Ulysses" , "Fabled one-eyed giant" , "One-eyed monster" , "Mythical creature" , "A one-eyed giant in Greek myth" .)