There's no heat or swelling or sign of an injury, so it's most likely an abscess, which has happened many times before, or it's a bruise. The only thing that will heal a bruise is time, so that's an easy fix. To check for an abscess, I pulled out my brand new hoof testers and squeezed for all I was worth. I have no idea how hard you really have to squeeze, probably harder than I can do, but he didn't react. I did notice that he didn't want to land on his heal during a trot out though, so I am guessing it's a brewing abscess.
Fingers crossed. Although for what I am not sure.