Looks like he has bumble foot too? He could have stumbled or tripped over something ducks can be pretty clumsy. I’d def get vet help if you can. Sprains can take a long time to heal. If that’s what it is then rest, water therapy and meloxicam (vet) can help. Also for support I’d get the liquid BComplex from TSC and begin giving that to him. Great for leg health. It will say injectable but just peel off the foil and use a dropper to put 1 ml over a tasty treat. Just enough treat he’ll get full dose. I’d do this 2Xa day. Ducks are amazing in healing hopefully with so TLC Olaf will be on the mend very soon. The Liquid B Complex is in the cattle dept.