Messi, 38, left his side's 6-4 Major League Soccer victory over Philadelphia Union in the 73rd minute, clutching the back of his thigh after a free kick.

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

Inter Miami manager Guillermo Hoyos had downplayed the issue after the match, saying Messi appeared fatigued after playing on a "heavy" pitch.

The MLS is pausing for the World Cup, which will be co-hosted by the United States, Canada and Mexico from 11 June to 19 July.

Argentina coach Lionel Scaloni included eight-times Ballon d'Or winner Messi in a provisional 55-man squad announced earlier this month, ahead of the defending champion's opening match against Algeria in Kansas City on 16 June.

Messi captained Argentina to its third World Cup title in Qatar in 2022 and is expected to lead the team again in what could be his sixth appearance at the tournament.