There is no way to determine what is wrong with your cat with out an exam, palpation and X-Ray. Please take your cat to the vet ASAP for these necessary diagnostics.
He may have a sprain or strain. It may feel like there is a hole if the ligament or tendon has pulled away from the bone. It could also be a fracture. These types of injuries can be bandaged or casted. A bad fracture may need internal or external fixation.
After roughly 3 hours- the hole dissapeared and the cat is only slightly limping wheras before he could barely walk> Thanks!