What a darling!
Looks like bumblefoot to me. You need to think about whether you can get him to a vet, but in the meantime and in any case, right away there are things you can do.
First, apply a warm Epsom salts compress to the foot for as long as the two of you can stand it. Five minutes good, ten minutes better, three minutes better than nothing. And I would start three times a day for this one.
Slather the foot and leg after the compress with triple antibiotic ointment (without pain reliever).
Consider oral antibiotics in case the infection gets into the bloodstream, going systemic, which can be serious.
Consider whether you want to open the foot to get rid of some of the chunky pus, but I don't like to do that - haven't had to, since we have been blessed to catch it early around here. Opening a duck's food vastly increases risk of infection. But then, you're already dealing with what I would call a serious case of bumblefoot, which is an infection.
There may be a splinter still in the foot. Epsom salts compresses help draw out splinters, but if you have someone with that kind of medical gift, have them look for signs of a splinter and remove it if found.
You might want to let him swim in lukewarm water for 20 to 30 minutes before applying the compress, to soften the skin a bit.
Keep him in a clean sick bay area with comfy bedding, fresh water and food. Consider putting some poultry vitamins in his water to boost his immune system.
