Messi, 35, led Argentina to glory last year in Qatar in what was his fifth World Cup appearance.
Although Messi repeatedly said throughout the tournament that it was going to be his last, Argentina coach Lionel Scaloni, his teammates and fans remained hopeful the seven-time Ballon d'Or winner could feature at the 2026 World Cup that will be played in the United States, Mexico and Canada.
In a report by Efe News Agency, Messi told Chinese sports outlet Titan Sports when asked about the 2026 World Cup: "I think not. [Qatar] was my last World Cup. I'll see how things go, but as it is right now, no, I won't go to the next World Cup."
Messi is on international duty with Argentina in China for their upcoming friendlies against Australia on Thursday and Indonesia four days later.
Messi had a starring role at the tournament in Qatar to end his wait for the only major honour to have eluded him in his career.
Messi netted seven times in seven games and became the first player to score in each round of the same World Cup since the round of 16 was introduced in 1986.
He scored twice in the final against France, which ended in a dramatic penalty shootout, to lead Argentina to its third World Cup title.
He also became the first player to win the Golden Ball award twice since it was introduced in 1982 (he won his first in 2014).