Tumor under chick's wing??

[Sc_chickengirl]

I just went outside and was cleaning my chicks brooder when I found one of my Sebright chicks was holding its wing weird and I picked it up and saw this.
Is it a tumor? I've never seen anything like this in my 10 years of having chickens. Is there anything that can be done for it?
Its very healthy otherwise so I'm hoping there is some way I can help it and won't have to cull it.
This chick is almost 3 weeks old and I had it out less than a week ago and it had nothing like this.

 

[JacinLarkwell]

Could be a tumor or other growth. I had a cockerel that had one at hatch. It didn't grow much with him, so by the time he was culled, it wasn't very noticeable other than a few gathers being wonky over the top of it