Gurgling, limping, and foamy green poop does NOT sound good. So sorry, don't mean to be blunt, but I have a feeling this is Marek's. If you do a search up in the search bar for "Marek's", you should be able to find some ideas for treatment. I've heard of chickens surviving, so who knows? But it's also possible that the roo has a broken leg or serious infection. Pick him up and wrap in a towel or blanket so that he is immobile. Then check both feet for splinters, thorns, or large abnormal lumps. Gently palpate his legs and stomach. If he flinches or signals that a particular area is tender or sore, check more thoroughly for wounds and record it. Once you have completely finished the outer inspection, open his mouth and check for any abnormalities, such as pus in the mouth cavity or inflamed areas. Make sure he is eating and drinking and getting vitamins from eggs or lots of greens. Watch for gaping or choking. Make sure you get him some electrolytes as well. Good luck, hoping your boy pulls through!