I think we all clean out the lint (or whatever) from our navel, but 99 percent of us don't bleed from the cavity. I believe it could be as simple as a pimple or as complicated as a tear in the lining of the stomach. I'm assuming that he can't see where the blood is coming from inside.

There's no doubt he needs to have a doctor check it out to make sure what it is causing the bleeding. We could speculate all day about the cause, but a physician is the only one he'd want examing that area.

Sorry I couldn't be more helpful but if the cause is hidden, it would be more dangerous to proceed without being examined. Hope everything works out.