Fiasco left unresolved to a degree (5)
I believe the answer is:
loser
'fiasco' is the definition.
(thesaurus)
'left unresolved to a degree' is the wordplay.
'left' says the letters should be written backwards.
'to a degree' says the answer is hidden in the clue.
'resol' is hidden in the letters of 'unresolved'.
'resol' back-to-front is 'LOSER'.
(Other definitions for loser that I've seen before include "One frequently failing" , "one that's been left behind" , "One not winning" , "One who frequently fails (colloq.)" , "One who is habitually unsuccessful" .)