Hello. Thanks for writing in. How long has this been going on for? How old is your cat? If you manipulate and move his joints in this limb, does he seem painful anywhere?
Thanks for the information. Usually when they don't apply any weight on a limb, it is usually an infection, fracture, dislocation or a very recent soft tissue injury. If the injury happened last night, I would expect him to be bearing some weight on the limb by now if just soft tissue, but that is not 100%. My biggest concerns is that he may have gotten into a fight and have an abscess forming in that limb. A fracture around the elbow joint or a dislocation there is still possible, even though he is not showing any pain. Cats will hide sickness and pain often. If he is positive for leukemia, I would be very concerned about his immune system being able to fight off an infection. In addition, leukemia positive cats are prone to a certain cancer called lymphoma. I would have your vet check this out today. They may need to get some x-rays, or, at the very least, prescribe a pain medicaton and antibiotics for him. Please let me know if you have any other questions. Hope this helps.
Cat Veterinarian
7 years of clinical veterinary medicine and 17 years experience caring for household pets.