Sorry about your rooster. How old is he? Are your roosts very high? It is hard to see both legs in the pictures to compare them for swelling. Is his foot or hock swollen compared to the other? Is he moving the leg, or does it seem numb or paralyzed? A vet could take an xray to rule out a break, and that would cost some money.
Sprains and broken bones can take weeks to heal, and rest is needed, in a pen or dog crate with food and water. Vet wrap and padding can be good for splinting. Make sure that he can reach food and water. Chicken slings can be helpful to use for several hours at a time, to get them upright and in front of food and water.
If the leg or foot seem more numb, then Mareks disease could be a problem. Usually, in that case, they may use their wings to get around and help balance. Check the bottom of his foot to look for a bumble foot scab, just to rule that out.