Does he live with another rabbit, who could have bitten him? Is it swollen, sore, or warmer than the rest of his skin (might indicate infection)? Does he scratch at it? Sometimes rabbits have mites or other skin problems and you can only tell because they scratch their skin so hard they hurt themselves.
For now you can put Neosporin on it, not Neosporin Plus because the extra stuff in it is bad for the bun to lick off. If it's possible that another bunny or other animal did this to him, keep them separate. Depending on how it looks and feels you may want to take him in to a vet on Monday.
Any way to get a better picture close up? I know that is difficult with most cameras...and I speak from experience. I had two thoughts. Like Naturestee, if this rabbit lives with another...maybe a bite....possiblysomething like a spider or bee or something like that.Another possibility...especially if the rabbit lives or goes outside...maybe a warble. We have seen more warbles this year than ever before....actually birthed one here a few weeks ago. Look at the center of the spot. If it is a bite, you might be able to see teeth marks or scratches. If it's a warble, you will see something move in the center every now and then. I also think I would take Naturestee's advice with the triple abx ointment just in case.
Could it be that she was scratching with nails that were too long? It had been a while since I cut them about a week ago. She lives with another female but they have lived together for about 6 months and have had no problems in the past. She hasn't been outside in a long time though. Here are a couple better pictures.