How old is the duckling?
My main concerns would be - keep it away from flies - I won't type that it large letters, because I do not want you to feel I am yelling, but it is so important to keep away from flies right now.
Next, longer term concern - infection - I would rinse with mild saline five or six times a day.
I am going to ask for others to check in - @WVduckchick @casportpony @sourland and see if they have had experience with this.
Ducks and ducklings are amazing in how they heal - I feel we need to know the best technique.
There is a bandage material that is used on people who lose a lot of skin - I don't recall the name of it - I think that might be the way to go, here.
But maybe we don't want to cover it. I would say not to cover it just now. And please do not use hydrogen peroxide or iodine on the wound. Saline solution, or Vetericyn spray if you have it.
Pain management is another thing we need to cover - ibuprofen is okay for ducks - don't know if the dosage (aside from adjusting for weight) needs to be modified for ducklings.
How is the duckling acting? Eating? Drinking? Pooping?
I need to leave the computer for a while - I will check back.