He may have been abandoned because of his symptoms or become hurt. I would quarantine him away from my other birds for at least a month in case of any illness he might have been exposed to. Treating with B complex vitamins 1/2 tablet daily crushed and put in a small amount of his food, such as...
I responded on your other thread about this rooster:
https://www.backyardchickens.com/threads/rooster-with-broken-leg.1589977/
Have you started him on the super B complex tablets yet? It can be hard to know whether he is injured, has a B2 riboflavin deficiency, or Mareks. I would read the...