Does it still not bother him? I've never seen anything exactly like that, but I wonder if it's something like thrush? It's probably not something that needs to be seen on an emergency basis, unless it's markedly worse tomorrow or you see signs of it starting on your lab, too, but I'm glad you've got an appointment this weekend!
Pls, let us know what the vet says about it--very curious as to what it might be.
And welcome to the board, Tharamis!
"We are--each of us--dying; it's how we live in the meantime that makes the difference."
"It's not what you gather, but what you scatter that tells what kind of life you have lived!"
"Be kinder than necessary, for everyone you meet is fighting some kind of battle."