Felt something in dogs hair on his back. Please advise?

Hi I have felt something in my dogs hair on his back and I thought it maybe was some hair clumped up from when I game him a bath so I thought I would just brush it out but after it wouldn't come out I took another look and noticed that I have scratched it and there was some blood so now I'm not sure what to do about it. Go to the vet tomorrow? Will he be able to give me an answer right away?