If you wrap, be careful not to cut off blood circulation. (worrywort me).
It really looks to me like the heavy-wing developmental stage, when the wing feathers are coming in and the wings droop because the muscles aren't used to the weight yet.
Just my feeling.
Here is an example of it...
I have seen a number of reports about this, I think it is a developmental stage for some ducks.
Just feed a good balanced diet, plenty of fresh water, decent bedding, keep them safe from predators, and keep an eye on him.
Please keep us updated on how they are all doing.