I had a hen that went from a limp to loss of leg use with no known reason. I separated her and gave her a special diet and she eventually walked herself back out to join the flock. No idea what caused it, or if what I was doing really fixed it or if it was time, but Ill pass on what I gave to squeecker.
First gave her lots of room to move, but also things to lean against. Checked on her constantly. Gave her V&E (vitamin and electorlites) in her water. Mixed plain yogurt with her food. Also squeezed a vitamin E tablet into her mouth nightly. gave her hard boiled eggs, some cooked oatmeal. Basically anything good for her and high in nutrients. It took some time, but she healed.
I hope your boy snaps out of it faster then mine.
Good luck
Shannon