It looks painful, but before you can see the vet tomorrow, it does not hurt to get it cleaned with peroxide and perhaps try a topical ointment.
As others said, please come back and update as it will be also helpful for others to find out what to do or what caused it.
Best of luck.
__________________ "You can say any fool thing to a dog, and the dog will give you this look that says, `My God, you're RIGHT! I NEVER would've thought of that!'" - Dave Barry |