Down on one's luck (4,2)
I believe the answer is:
hard up
'down on one's luck' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for hard up that I've seen before include "Having little money, almost skint" , "'In great need (4,2)'" , "Informally short of money - that's tough" , "Strapped for cash, it's tough" , "It's not easy to be in straitened circumstances" .)