He has a head injury of some sort. It is impossible to know how serious until tests are completed (unless something bad happens, like him slipping into a coma). Those tests take time. The brain is a delicate organ. If he breaks a bone or tears a ligament, the damage is much more obvious. If there's obvious damage to the brain, that's not a good sign. The best-case scenario is a battery of tests that don't find any long-term damage, with everything filed under the general heading of "concussion". That can take some time.
I just have the feeling that if they find something quickly, it means they found something serious, so it's better if we don't know for sure what's wrong before lunchtime tomorrow.