If he is moving around a lot I would try putting him outside with his buddies for a little bit. Spending time outside may encourage his appetite. Hopefully you can get him to eat on his own. If he is drinking fine, but not eating, then he might be able to go a bit longer without tube feeding. But if he continues to not eat, he will need tube feeding.
The fact that he doesn't hold his head up much does concern me, because it could be a sign of reduced nutrition. With him swimming around and being so active makes me think it could also be just the neck injury. I would consider adding some vitamin E into his diet to help his neck strengthen. It is usually used for wry neck, and it won't hurt him. Herbs contain vitamin E. Here are some good choices : cayenne pepper, oregano, basil, sage, thyme, parsley, cloves, cumin, caraway, cinnamon, marjoram, and turmeric.