What's the likelihood of this being a Zymbal's tumour vs. just an abscess?

[anyreception]

More context: it feels rather hard and seems painful, he squeaks when I touch it. No scab at the moment, it looks under the skin. It happened very very suddenly, like even less than overnight. He's still behaving normally and shows no other symptoms. I've had another rat with an abscess in this area that went away so I really do hope it's that but this is quite large, and got a bit larger in the last day. I'm taking him to the vet soon but wondering if anyone has experience with this. He's 8 months old

 

[Kye]

More context: it feels rather hard and seems painful, he squeaks when I touch it. No scab at the moment, it looks under the skin. It happened very very suddenly, like even less than overnight. He's still behaving normally and shows no other symptoms. I've had another rat with an abscess in this area that went away so I really do hope it's that but this is quite large, and got a bit larger in the last day. I'm taking him to the vet soon but wondering if anyone has experience with this. He's 8 months old

A top down view would help a ton, its more likely a tooth abscess than a zymbal's tumor because of the age but I wouldn't rule anything out