Not all press agents look tired (3)
I believe the answer is:
sag
'look tired' is the definition.
'not all press agents' is the wordplay.
'not all' indicates a hidden word.
'SAG' is hidden in the letters of 'press agents'.
(Other definitions for sag that I've seen before include "Droop, sink in the middle" , "Sink under weight" , "fall" , "Lose energy" , "Fail to retain interest" .)