guinea pig lump

New to this forum, I've attached an image of what I saw on my guinea piggie a few days ago - this has grown this big since a week and a half ago, I have an appointment with the vets tomorrow afternoon but I'm worried for my piggie 😭 It bleeds when you touch it, it appears to be painful for him...

I have a six year old male gpig Gibby, and a four month old female Alaska. They are in separate cages obviously! :) we got our new little lady last month totally unexpectedly. We went to Petco to get supplies for Gibby and our other pets and stopped to quickly look at the babies they had...