So… if one of your thoughts was that his shoeless hoof was cutting his belly that would have been my response is to wrap the hoof to prevent it from happening. So I did happen to read your statement, no need to be rude about it.
If you can’t find the cause of the problem, a vet call may be the response, they are really good at examining a scrap or cut and being able to eliminate possibilities of cause. Almost like a detective in discerning a scrap from wood versus a bite from a brown recluse spider. <– Even though that was an obvious huge difference in type.
Unless you want to try bubblewrap. Good luck!