I am happy to try. I just wish I could be more help. I agree it is not his crop and hope someone else here has an idea of what it is and how to address it.
I am so sorry that I am unable to help! Do you know how quicky this came on? Is the mass warmer to the touch than the rest of him? It does not appear pink (like infection) in the photo. This is an odd one. I hope someone here is able to help.
I slso see his comb is turning blue. There are no respiratory symptoms whatsoever? No open mouth breathing? The fact that it is perfectly spherical also seems like it could be a cyst of some kind?