Withdraw when about to get weary (6)
I believe the answer is:
retire
'withdraw' is the definition.
('retire' can be a synonym of 'withdraw')
'about to get weary' is the wordplay.
'about' becomes 're' (regarding).
'to get weary' becomes 'tire' (I've seen this before).
're'+'tire'='RETIRE'
'when' acts as a link.
(Other definitions for retire that I've seen before include "Go to bed or quit work for good" , "Withdraw - give up work - go to bed" , "Leave job permanently (6)" , "Stop climbing the ladder" , "Stop work - go to bed" .)