Look defeated - day turning not so good (5)
I believe the answer is:
droop
'look defeated' is the definition.
(to droop is to look sad)
'day turning not so good' is the wordplay.
'day' becomes 'd' (abbreviation for day).
'turning' says the letters should be written backwards.
'not so good' becomes 'poor' (of less good quality).
'poor' backwards is 'roop'.
'd'+'roop'='DROOP'
(Other definitions for droop that I've seen before include "be despondent" , "Sag downwards" , "male problem?" , "Sag wearily" , "Go limp" .)