Both comrades injured, so out of action (4,2,6)
I believe the answer is:
hors de combat
'out of action' is the definition.
('hors de combat' can be a synonym of 'out of action')
'both comrades injured' is the wordplay.
'injured' indicates an anagram.
'both'+'comrades'='bothcomrades'
'bothcomrades' with letters rearranged gives 'HORS DE COMBAT'.
'so' is the link.
(Other definitions for hors de combat that I've seen before include "Out of action due to injury" , "Disabled, out of the fight" , "Injured and out of action (French)" .)