It looks like the fur was pulled out and the top layer of skin came with it. Has there been humping? That would be my first thought, especially since you can see new fur growing in.

The wound may not have healed properly. I am not experienced with major wounds, so my best recommendation is to see a vet so the wound does not get worse.

I do not think the cause of the wound is a disease though. At least initially until there’s some more information.

How long have you had your rabbits ? Are they housed together and if so, how long have they been together for? Can you explain when you got them, if they’re fixed, and when you put them together if that’s the case?

If I remember correctly, rabbits will bite on the back of another when mounting, and this can lead to injuries.

If you have any suspicion that your male may have caused this, separate the two rabbits immediately. Perhaps you’ve seen them scuffle or chase each other, and this is a sign of an unhealthy bond between rabbits. Unhealthy bonds will have frequent/sporadic fights from what I’ve read, and this is dangerous.

I do not know the details until you reply, but to let you know immediately, if these are two rabbits you have had together since they are young, it’s possible they are old enough that they are hormonal. Hormones will make “childhood rabbit friends” forget that bond, and they will fight. To resolve this, the recommendation is to have both rabbits fixed (neuter/spay) and keep them separated until that’s done. Once they are both fixed, you go through a bonding process, which is outlined on this website’s BUNNY INFO section.