If you release him he isn't going to make it. Ducks have a hard enough time evading predators when they can walk normally, one that is having difficulty will be picked off fast.
If you can't keep him can you find a waterfowl rehabber that might take him in? Are you in the USA?
If you could get some liquid b complex that works so much better when one has lameness than even Nutritional yeast and brewers yeast.
Bless you for saving his life but he still needs protection.This will show you what type of liquid B complex to get.
https://www.backyardchickens.com/threads/niacin-deficiency-in-waterfowl.1367557/

If you can't keep him can you find a waterfowl rehabber that might take him in? Are you in the USA?
If you could get some liquid b complex that works so much better when one has lameness than even Nutritional yeast and brewers yeast.
Bless you for saving his life but he still needs protection.This will show you what type of liquid B complex to get.
https://www.backyardchickens.com/threads/niacin-deficiency-in-waterfowl.1367557/
