You must keep him separated from the others until this heals up.
Put some healing cream on it like triple antiobotic, or niesporin. These will keep the wound miost and lrevent fly stike and drying out.
My guess is your chicks may be crouded. Can you give us a picture of your brooder or coop set up?
If you can use some wire mesh and section a place inside the brooder so this chick is still with the group, but not accessable to them. This will make it easier to introduce him back to the flock. And one chick quarentined by himself is to lonesome, chickens are flock animals.
Good luck and keep us updated.