IF the floor is wire, that could be the issue; a snagged toe or toe nail - do the nails need trimming? Rats, cats, coons, weasel, fox...all can injure through wire bottomed/sided cages.
Are you where it is cold? Could fur have frozen to wire and torn off? If you are in a cold climate, no flies, then likely best to cleanse it as advised, soap, not detergent (no HP, or alcohol) hibitane, or dexatin 4 (chlorhexidine) is ideal. Then leave open to the air and ensure floor is clean, lined with
wood stove pellets for bedding (easy to separate the soiled areas keeping cage clean during healing. I am leery of using ointment, as they tend to lick it off; the licking can prevent healing, and ingestion of ointment could have negative consequences (without knowing the ingredients, I can't say for sure).
If it is a warm climate I would move him indoors (provide the same substrate of
wood stove pellets) to ensure it is not bothered by fly eggs (
maggots) or other issues high heat or humidity will cause with an open wound.
Watch closely (take photo's daily for comparison) soak in very warm water with Epsom salts at least once daily until healed over (no raw flesh is showing). The salt water will draw out excess fluids and infection that could be brewing.
Rabbits DO tend to form hard pus, not liquid. At the first sign of increased redness or swelling, you will need to hit the vets for oral antibiotics. If it is a bite or claw, you may want to do this regardless due to the high risk of infection.
Good luck, hope it turns out to be minor and heals quickly.