BUENOS AIRES, May 25 (Xinhua) -- Argentina captain Lionel Messi was diagnosed with muscle fatigue in his left hamstring on Monday, less than three weeks before the start of the FIFA World Cup.

The 38-year-old was substituted in the 73rd minute of Inter Miami's 6-4 MLS win over Philadelphia Union on Sunday, having shown discomfort after taking a free kick.

Subsequent tests indicated the former Barcelona and Paris Saint-Germain forward suffered "overload associated with muscle fatigue", according to an Inter Miami statement.

"The timeline for his return to physical activity will depend on his clinical and functional progress," it added.

After the match, Inter Miami manager Guillermo Hoyos said Messi had felt tired after playing on a "heavy" pitch.

The World Cup will be staged in the United States, Mexico and Canada from June 11 to July 19.

Defending champion Argentina will begin its campaign against Algeria on June 16 before also facing Austria and Jordan in Group J. ■