Could be an unabsorbed yolk, could be a swollen or infected navel, just a "rough" navel, or as you say, possibly even a hernia with protuding intestines where the abdomen didn't seal together.
Is it large or small, and what color is it?
Pictures would help a lot, is that possible?
When I have one hatch that looks questionable in the navel area, I dust it with tetracycline powder and keep it in the incubator a while longer, but make sure it has water and food if it will take it. I had a quail hatch last month that actually did have intestines outside the body, and obviously didn't make it. But, there is a fairly decent chance that it will be ok.
Be sure that there isn't anything rough in the incubator that it can pop it on, in case its unabsorbed yolk, because they can die quickly if that happens (they bleed to death).
