The pictures provided allow very little visualization of the leg so it's hard to make out what might be the problem - from what I can see it does appear abnormal, and could be the result of a nutritional deficiency, an injury, or a malposition that occurred during the incubation period. Over the internet, it is hard to say which of those it might be.
Considering the problem is the result of the former condition mentioned, you could start the bird on a poultry vitamin for a week or two and see if there are any improvements. Keeping the duckling on padded grouds with plenty of traction would be suggested. Hopefully, the angulation in the leg will correct itself.