My guinea pig has a lump on his leg. Does anyone have experience about this?

He is five years old so I am worried it might not be safe for him to have surgery. Do you think it should be removed? Years ago I had a guinea pig about that age who had surgery on a tumor by his nipple and was okay. But it took him a while to wake up after his surgery. So I don't know what I should do. I have been watching it. It bled some but it isn't any more. Unfortunately I have to wait until next month to go to the vet but since it doesn't seem to be an emergency I think it will be okay. This month is bad for money or I would have rushed him there. He is able to walk okay but I don't know if he is in pain. Has anybody had a guinea pig who didn't have surgery for a lump? Was he okay with it left there?