Hi ,i really dont know the cause as next to this bunnies cage their is a female who gave birth recently , also this Bunnies mom and her siblings none of them have scabies , maybe she bit the poor boy as she is a bit temperamental but on the contrary the wound day by day is increasing which leads me to suspect scabies , sadly i dont know how to inject but i am applying Fucidine ! What else should i do to cure it asap , if you have anything in mind do let me know .Do you know the cause? Was he bit or in that location I would suspect a tooth problem. Is he eating/drinking ok? I would clean daily with a gentle soap and water, then a OTC triple anticbiotic cream and a shot or two of penicillin.
Just my opinion I would not suspect it to be scabies unless there are other affected areas or bunnies. I believe Ivermectin will treat scabies. (They're a skin mite)