A foot co-unit made hors de combat (3,2,6)
I believe the answer is:
out of action
'hors de combat' is the definition.
(synonyms)
'a foot co-unit made' is the wordplay.
'made' indicates anagramming the letters.
'a'+'foot'+'co'+'unit'='afootcounit'
'afootcounit' with letters rearranged gives 'OUT OF ACTION'.
(Other definitions for out of action that I've seen before include "Not operational" , "Not working" .)