Dear XXXXXXXX,
If he is not putting any weight on it at all, after 4 hours, he needs to go to the vet now.
The reason being, the non-weight bearing can indicate a fracture or a ruptured ligament in the knee.
Usually if it is just a sprain they will put weight on it.
Veterinarian
Veterinarian in practice for 10 years. Compassionate, Caring, Experienced.