All ducklings will be very wobbly for the first few days, and they will also be super sleepy.
Do you have any Niacin? When he starts drinking water, I would make sure to add that. Get the regular kind, not the timed released, and add one capsul to every gallon of water. What I did with my last ducklings was just take a gallon jug, fill it with water, add the Niacin, and just pour the water into their drinking bowl. Make sure you just add the powder, though, not the actual capsul shell.
EDIT;
Oops, forgot to add that Niacin is used to prevent leg problems, which is why I suggested it, since you seem concerned. You can also use Brewer's Yeast, but make sure it's actually BREWER'S Yeast, NOT baking yeast.