Are the sores right on the foot pads? My dad raises rabbits and we always kept a wire grate on the bottom to keep them from developing sore hocks. Thats when they get something that looks like an open sore on the bottom of their back feet. If you put a flat surface they can urinate on it and when they sit on that area it can irritate the foot causing sore hocks. That's why he always wanted the bottom of the cage to be open so any urine could fall though the cage. But I've also never had pet rabbits so maybe they use a litter box in their cage and wouldn't pee on their rug.