@powrpuff Welcome to BYC and Congrats on your new duckling.
I want to give you some great info on caring for your duckling. http://www.backyardchickens.com/t/750869/raising-and-caring-for-ducklings#post_10611711
Now to the foot, could his/her foot gotten stepped on by accident? It looks pretty bruised and they can get under foot pretty quick. I'd just keep an eye on it as long as nothing feels or looks broken. You can also soak the foot in some warm Epsom salt water I'd use a cup for the lil one and make sure he doesn't drink out of it [Epsom salt is also a laxative] but great for swelling and bruising. Half teas to 1 cup of warm water. and please if your letting the little on swim make sure the water is warm when they are only in down they have no way to control their body temp and can chill very easy. They also need to be kept at temps from hatch at around 85* then drop that temp 5* each week there after till same as house temp. This info will be your best guide to keeping your duckling healthy and happy.
Edited by Miss Lydia - 3/4/16 at 5:05am