Chickens can get squamous cell cancer and this looks like it may be one. It looks like it can be removed, but would need to be done by a professional. At this location leg muscles, nerves and blood vessels are easily injured which can cause the leg to be useless (nerve damage) or worst case, the chicken can bleed to death. Also imagine the pain if the chicken is not anesthetized!! I wouldn't do that to my worst enemy. You need a vet. Reach out to your nearest vet university for help.