Argentina’s World Cup defense has been hit by a major injury scare just three weeks before the tournament kicks off, with captain Lionel Messi suffering a hamstring injury during his final club appearance for Inter Miami.

The 38-year-old superstar was forced off in the 73rd minute of Inter Miami’s chaotic 6-4 Major League Soccer victory over the Philadelphia Union on Sunday. Messi was seen clutching the back of his left thigh immediately after taking a free kick.

Following a round of diagnostic evaluations, Inter Miami released an official update on Monday confirming the nature of the injury.

"After undergoing further medical tests this Monday, the initial diagnosis indicates an overload associated with muscle fatigue in his left hamstring," the club statement read. "The timeline for his return to physical activity will depend on his clinical and functional progress."

The diagnosis offers a sliver of hope for Argentina fans, as a muscle "overload" typically indicates severe fatigue and tightness rather than a full structural tear, which would have instantly ruled him out of the tournament. However, with the World Cup less than 20 days away, the tight recovery window will severely test the veteran forward's fitness.

The update comes after Inter Miami coach Guillermo Hoyos initially attempted to downplay the severity of the issue post-match on Sunday, attributing the substitution to general fatigue caused by a "heavy," rain-soaked pitch.

The MLS is now pausing its season as global attention shifts to the World Cup, which is being co-hosted by the United States, Canada, and Mexico from June 11 to July 19.

Argentina coach Lionel Scaloni, who included the eight-time Ballon d’Or winner in his provisional 55-man squad earlier this month, will be sweating over his captain's availability. The defending world champions are scheduled to open their tournament group stage against Algeria in Kansas City on June 16.

Messi famously captained La Albiceleste to their historic third World Cup title in Qatar in 2022. This upcoming tournament is widely expected to be his international swansong, marking what could be a record-breaking sixth appearance at a FIFA World Cup. All eyes will now be on Argentina's medical staff in Buenos Aires as they race against the clock to get the legendary number 10 match-ready.