As far as I can tell it's some kind of discoloration. It's not raised nor does it really feel different to the touch than the rest of his skin. Here are some close up photos. Hes really squirmy and unhappy with me so I did the best I could
So it looks swollen to you? I thought it did from some angles but wasn't sure. Mr Peaches is very well-loved by us. Hes so handsome and unique looking. Saxony coloring but definitely seems like he has some runner duck in him. I assume he was dropped off in the neighborhood by someone or at least handled as a baby because I'm able to hold him without him freaking out too much. I hope I can get him healed up quickly, he has three girlfriends who I'm sure are wondering where he is!
Thank you! I was wondering if I did the right thing because I'm still fairly inexperienced with duck medical care
I can try putting the crate out after he's rested up and see if they come! I have a duck pen out back that is occupied by an Australian spotted male who doesn't have much use of his right leg and can only somewhat walk on the hock (Vet had us try building a therapy wheelchair for him...he was NOT impressed) and a muscovy we found in the road as a duckling who was part of a clutch one of our other neighborhood ducks gave birth to with a really bad head injury. Didn't expect him to make it but now I have a giant male muscovy two chickens on oral medications...and now Mr. Peaches has decided it's his turn in my animal hospital! It's so stressful and overwhelming at times and I'm learning as I go...I kind of unexpectedly ended up as a poultry caretaker 
but, I love them all so much and can't imagine life without them, so I'll do whatever I have to do 
thank you!
. I just want to echo @Miss Lydia that rest and good nutrition are the most important things right now. It looks like he’s unwilling to put any weight on it? That makes me think it might be more serious than a sprain. But letting him rest a few days and waiting to see if it gets better on its own shouldn’t hurt!
