Strange wound

I have just found a wound on the inside of Dylan's thigh. I can't work out what it is. It's a very strange place for a bite and it looks more like something has either burst or entered the skin. It bothers him, it is bleeding and the area of the size of a 50 p coin around is very inflamed. I am stumped. I have cleaned it up and will see what happens with it over night and if necessary take him to the vet tomorrow.