The comments come as Messi prepares to make his debut for Inter Miami, whom he joined on a free transfer after parting ways with Paris Saint-Germain in June.
"Logically, because of my age, it [retirement] won't be far away," the 36-year-old said in an interview broadcast on Argentine television.
"I don't know exactly when that moment will be. I'm just taking things day by day and enjoying all of this that we are experiencing."
Messi admitted he had achieved everything he had hoped for in football after leading Argentina to World Cup glory in Qatar last December.
The Albiceleste captain scored two goals in the final and won the Golden Ball awarded to the tournament's best player.
"I think it will happen when it has to happen," Messi said of his retirement from international football.
"After having achieved everything in recent times, the only thing left is to enjoy it."
Messi is expected to make his debut for Inter Miami in a Leagues Cup match against Mexico's Cruz Azul in Fort Lauderdale on July 21.
