Matted fur and potential lump

[Laura M.]

My guinea pig has a matt of fur on his cheek/neck. Initially, I thought it was just matted because he was unable to clean it (he has a swelling on his foot, which the vet prescribed a spray and painkillers for). Today, I had a closer look because I thought it was a bit worse than before - I've had a guinea pig with long hair which frequently matted before, but when I pinched the skin gently, it just felt like normal skin, but this time it feels like a lump going way deep down to the skin. It's hard to describe. I'm not sure if it's just a bad matt, or maybe a lump with hair growing out of it, or a lump secreting something, causing the fur around it to matt.
The matt is very small, less than half the width of a pencil, and the "lump" which I can't tell is a lump in the skin or just a matt of hair, is about just less than 1cm diameter.
My apprehension is because this issue was present on Wednesday, when I took my guinea pig to the vet, and they didn't spot this - that vet trip cost me £90, and I am understandably upset that it's going to cost us another £90 just because they missed something.

 

[Piggies&buns]

I’m sorry to hear this.

When you go back to the vet, it will cost another consultation fees (plus any cost if any necessary further investigation and treatment).

Any lump does need a vet to check it.

I hope he is ok

 

[weepweeps]

Good luck at the vets I hope it’s something easily treatable.