With the unknown here, if it's moving it at all, that's a good sign. It could have sustained an injury being moved around from truck to pen, and hopefully it's not an internal injury to the bone.
Just in case, if you have some B-complex, as in human pills, I'd grind up 1/4 of one for him, and mix it in a small amt of mash, so he eats it all. Just once a day for a week or two. If you don't have any and want to buy some at Walmart or drugstore, it's a lot easier to administer the liquid B-complex. The one we have, a full human dose is one eyedropper full, so for him, I'd go a 1/4 of that. If it's a little too much it's okay. B is one thing that just clears their system.
You could design a little chicken chair for it. What we did for one little one was stretch a piece of cloth over a coffee cup with a tight rubber band. Then guestimate where the legs will go through and use a sharp knife and scissors to create two leg holes. Push the cloth down just a bit into the cup before putting him in it. I would keep him in that for a few hours a day so he rests it. Be sure to offer him mash or dry, and water every so often while he's in there.