Don't let him lick it! As I write this my dog Daisy is getting reprimanded for licking her paw (yes, really).
Seven years ago she stepped on a piece of metal flashing roofers threw off the side of the house. She cut her front pad pretty good. A trip to the vet and she was fixed right up, so I thought. Left alone she licked and licked her paw until it was raw and bleeding, on the top. She couldn't reach the bottom, so licked the top.
I got her an e-collar (cone from vet, Elizabethan collar not shock collar), but it wasn't big enough, still licked. I needed a bigger one, but it was too late the damage was done. To this very day, she will lick her paw raw to bleeding, if left unattended and nervous. Apparently the physical scarring is gone but the mental and emotional scaring is still there.
I have the biggest e-collar (cone, Elizabethan collar) I could get for her to wear when we are out. Don't let this happen to your dog! Granted Daisy was picked from the litter for looks not smarts. Seven years later she will still lick her paw raw, probably to the bone, if I let her.