Total mismatch. Navy seals, first of all, have superior mental toughness. You are not going to defeat a Navy seal in hand to hand combat unless he's old or injured or you have a good weapon. Navy seals are trained to kill and survive life and death scenarios, and they are very good at it.
All things being equal a very average MMA fighter could probably go a while but in the end you are fighting an opponent who will never tap out, is physically and mentally tough, and there's no luck involved.