Rooster has air under skin on chest and has difficulty swallowing

[Katie Scarlet]

So what's happened is that the air sac has been torn during the attack. You need to keep draining the air out so the airsac can heal. You may need to drain it multiple times a day if necessary.
I found a video that will help, I know it's a pigeon but pigeons and chickens are very similar internally so it will be much the same

Hopefully the link works. I wish you all the best

Thanks I will give it a try a couple times a day. It looks just like this poor pigeons chest.

 

[casportpony]

I have had to do that repeatedly for a couple weeks and it refills.

Hopefully it will heal on it's own then.