SOP for knee injuries is for the doctor to examine, and if an injury may be present, he will order X-rays. These won't show anything in soft tissue, but are generally a prerequisite to MRI. A lot of this delay actually allows initial swelling to go down and most minor tears and sprains will clear up on their own.
Keep ice on it and see where your range of motion goes. If strength and feel return to normal, I'd just call it good. If you develop further swelling, a click or catch, or serious weakness in any plane, then you have a legitimate concern. Meniscus injuries are often left alone anymore unless they show grade 3 tears or cause other problems. Tendon or ligament separations are another matter.