Exhausted swan found in the road (5)
I believe the answer is:
spent
'exhausted' is the definition.
('spent' can be similar in meaning to 'exhausted')
'swan found in the road' is the wordplay.
'swan' becomes 'pen' (pen is a kind of swan).
'found in' is an insertion indicator.
'the road' becomes 'st'.
'pen' going into 'st' is 'SPENT'.
(Other definitions for spent that I've seen before include "Paid out - finished" , "Used up; exhausted" , "Completely exhausted" , "(Of resources) exhausted" , "Worn out having paid out money." .)