Lionel Messi was substituted in the 73rd minute of Inter Miami's 6-4 win over the Philadelphia Union on Sunday after clutching the back of his thigh.
Inter Miami head coach Guillermo Hoyos said the move was precautionary. He cited fatigue from playing on a heavy pitch as the likely cause.
"We don't have a medical report on that yet... He was genuinely suffering from fatigue," Hoyos told reporters. "When in doubt, the standard approach is always to ensure you don't take any risks."
The MLS season now pauses for the 2026 World Cup, which the U.S., Canada, and Mexico will co-host from June 11 to July 19.
Argentina head coach Lionel Scaloni named Messi in his initial 55-man squad on May 11. He must trim it to 26 players by FIFA's June 1 deadline.
Messi led Argentina to their third World Cup title in Qatar in 2022. They open their title defense against Algeria in Kansas City on June 16.