is there a way to isolate him within the chicken area? perhaps in a dog kennel? so they can keep looking at each other for a few days before being re-released?
do you have apple cider vinegar handy? spray everyone with it, either now or a bed time. Sometime this helps diffusing squabbles because then everyone smells the same.
(don't need to soak them, just a good spray - i put mine in an old windex type spray plastic bottle)