No, you can play with one. The AI opponents are terribly smarter than your AI allies, because it's supposed to challenging with 4 players, but if you're there alone, you'll just lose. So it's possible, but the odds against you are horrible. I've been in several games by myself & despite my best efforts, we lost. Some games I'd start alone & then others join just before losing & we're able to turn it around & win.