Plain Niacin capsule in a gallon of water will help. Keep a pan of water around him, something deep enough he can soak in. It'll feel better for him to soak and have the weight off his leg. Another helpful thing to try is tumeric. You can buy the spice and gently sprinkle it on his food. It helps with inflammation. I sprayed my ducks food with water and applecider vinegar then sprinkled the tumeric on it. I noticed the spice falls to the bottom of the dish, so spraying it lightly helped it to stick to the food.
Another thing is half a cup of epsom salt to a gallon of warm water. Soak him in it without letting him drink it as its a laxative. My rouen had a thorn in her toe and it swelled up and got infected. These were a few things that helped.