Keep him seperated. I would give him extra probiotics, vitamins, the works. Is it at all possible he could have a selenium or vit B defficiency? Is he eating crumbles or pellets - if he's a little guy he might have a hard time with pellets.
This is what happened to a friend of myn, her bird was vaccinated for Mareks and didn't show the normal progression of symptoms, but just went from stumbling around to just not using her legs - but was otherwise totally fine. She made a full recovery after switching to crumbles, adding some raw goat milk (loaded with probiotic bacteria, protein and fat) and vitamins. After a week of this treatment her hen was just fine. Her hen was even still laying eggs while not being able to use her legs much, so it sounds very similar to how your little rooster is acting. Hers was like this for over a month (and a vet visit) as well.
This is what happened to a friend of myn, her bird was vaccinated for Mareks and didn't show the normal progression of symptoms, but just went from stumbling around to just not using her legs - but was otherwise totally fine. She made a full recovery after switching to crumbles, adding some raw goat milk (loaded with probiotic bacteria, protein and fat) and vitamins. After a week of this treatment her hen was just fine. Her hen was even still laying eggs while not being able to use her legs much, so it sounds very similar to how your little rooster is acting. Hers was like this for over a month (and a vet visit) as well.
