The ability that defines Crusader of Odric's power and toughness works in all zones, not just the battlefield.

As long as Crusader of Odric is on the battlefield and still a creature, its ability will count itself.

Because damage remains marked on a creature until the damage is removed as the turn ends, nonlethal damage dealt to Crusader of Odric may become lethal if other creatures you control leave the battlefield during that turn.