Sounds like he might have sprained his leg or has some arthritis. You need to get him to a veterinarian to see that nothing is embedded in the foot or leg, that he has nothing wrapped around his leg such as fishing line or other material, or that he has not suffered a fracture.

In the event that he is able to get going after awhile, it almost sounds like he might have incurred an injury that has not fully healed or may have some arthritis. In any event, the veterinarian may be able to prescribe something like medicam which might help improve his leg. If your veterinarian does not know the dosage, you can submit to this post with your veterinarians name and contact number. This site's administrator can contact us directly and we'll supply the info to your veterinarian. We hope this helps. The Regal Swan