Substitute possessed by Rangers at Zagreb (6)
I believe the answer is:
ersatz
'substitute' is the definition.
('ersatz' can be a synonym of 'substitute')
'possessed by rangers at zagreb' is the wordplay.
'possessed by' indicates a hidden word.
'ERSATZ' is hidden within 'rangers at zagreb'.
(Other definitions for ersatz that I've seen before include "Mock" , "Imitation (from Ger.)" , "Made in imitation - in Germany" , "being of inferior quality" , "Imitation, not the real thing" .)