If a buddy is riding your bike with no insurance and hurts himself who covers the medical expenses?

Technically, your buddy covers the medical expenses. He might be able to have his medical insurance cover it depending on the injuries AND as long as he DOES NOT mention that he got hurt while on the bike. Once he says that the doctors will not treat him for those injuries because they can't bill med insurance.. Medical insurance companies don't want to be paying for injuries that happened on an auto.