Men brought back horse for a music producer (5)
I believe the answer is:
organ
'a music producer' is the definition.
(I've seen this before)
'men brought back horse' is the wordplay.
'men' becomes 'OR' (military abbreviation for other ranks).
'brought back' says the letters should be written backwards.
'horse' becomes 'nag' (term for an old horse).
'nag' back-to-front is 'gan'.
'or'+'gan'='ORGAN'
'for' is the link.
(Other definitions for organ that I've seen before include "With prompt enthusiasm" , "Body part - wind instrument" , "Functional unit of the body and musical instrument" , "means for communicating information" , "Brain, for example - instrument" .)