Lionel Messi's inclusion in Argentina's official 26-man squad for the 2026 World Cup, announced on May 29, anchors the market's 99.1% implied probability for a "Yes" outcome. As defending champions and record six-time participants, Messi and his teammates have begun preparations in the United States, with recent training reports and team arrivals reinforcing his expected participation despite minor pre-tournament injury concerns. Historical precedent favors his availability given his central role under coach Lionel Scaloni and prior statements expressing desire to compete. Realistic upset scenarios remain limited to a significant injury sidelining him before or early in the group stage, though the timing of squad finalization and ongoing fitness updates make such a development unlikely at this stage.