I hope you've fixed the vulnerability in your coop.
Your rooster could have a spinal injury. He may also be suffering from shock from the attack. Treat the shock with a cup of water with one teaspoon sugar and a pinch of salt and baking soda. Dip his beak so he will be encouraged to drink it.
Treat the possible injury with vitamin E capsules, one per day directly in his beak, and then give cooked egg with it. Do this for one week or until he's able to lift his head again. Also get some vitamin B complex and give him one tablet each day for the next two to four weeks. Stop it when he appears to be acting normally again.