Its unlikely to get infected, as long as his makeshift cup is kept clean. It should close up pretty fast.
The fluff will gradually cover the naval area, you'll need to very gently part the down to check on the area, avoid touching the open area though, because infection is still a possibility.
I'll be going to sleep soon, not sure your timezone, but hopefully there will be good news in the morning.
I'm going to @ a couple of people who might be around to help incase there is any change or any other concerns.
@New duck mommy 2021 @WVduckchick