Alright, time for an update. So sorry for everyone who has been waiting. Husband got home late yesterday, so I ended up trying to see what was inside of the mass this evening. We've been very busy. Now, he was holding his head up this evening, but the mass did not seem any smaller. He also is no longer lethargic after being brought in from the coop. I think he wasn't able to get to the water and food efficiently with the mass weighing him down. I have him in his very own cage now with food and water directly at ground level so he can reach both.
I first tried lancing it with a needle, but nothing came out, not even blood. So then I used a small scalpel to cut a very shallow slit that was no more than 1/2 a centimeter in length (I wanted to keep it as small as possible, to avoid infection and prolonged healing) Once I got past the outer skin layer and into the ball itself, it was very hard and a little blood came out. There doesn't seem to be any liquid, pus, or anything like that. It just seems like thick fatty tissue, which leads me to believe that it is indeed some type of tumor. I cut a little deeper to see if maybe it was just thick pus or simply another layer, but beneath that just seems like more fatty tissue. I don't think he could feel what I was doing, he only reacted to being restrained, not the cutting or lancing.
So now I'm kind of stuck. If he continues to do well, I may just keep him separated and see how it goes. I don't want to risk putting him back with the other birds if he may be contagious. I have no idea. If he goes back to being lethargic or the mass seems like it is keeping him from living a normal life and he is suffering I will consider culling him, though I would hate to have to do that. Thank you to everyone who passed along advice and knowledge, I really appreciate all of it. If you have any other suggestions or thoughts, please let me know.