I'm not sure but it definitely needs to be looked at by the vet. Does your vet use email? If so, email the picture to the vet and ask. The vet will want to see the cat in person anyways so call and make an appointment.
Sorry it took me so long to see this. What I'm looking at could very well be an abscess, or even a tumor. I'm not saying it is either of those, but the chances are good. Whatever it is, it is definitely going to require a vet's attendance and treatment.
PLEASE let us know how your cat is doing, and what the vet says!
I agree with my fellow team members that it definitely needs to get looked at. An abscess would be my guess (just a guess, I’m not a vet), in which case, I think, the vet might need to drain it, and/or give antibiotics.
Sorry for the late reply! I took him to the vet and it turned out to be gingivitis. The vet prescribed an antibiotic and right now he is much better. Thank you all.