Feckless person exhausted (8)
I believe the answer is:
deadbeat
This clue is a double definition.
'feckless person' is the first definition.
(a deadbeat is a useless person)
'exhausted' is the second definition.
(I've seen this before)
(Other definitions for deadbeat that I've seen before include "Disreputable person" , "Exhausted - layabout" , "extremely tired" , "idle so-and-so" , "Lazy, useless person" .)