My daughter just noticed this strange growth/injury on one of our ~4 week old SF buns. It's behaving normally. There is no evidence of profuse bleeding, and none of the other rabbits have any similar issues. For now it's quarantined.
Also, put out rat traps ... that is a bite wound and you may have rats/skunks/raccoons visiting at night. It should heal up on it's own, and the poor little one will always have a hairless scar on his nose