Pochettino, who is well aware of Messi's game-changing abilities having worked with the 35-year-old last season, said he was still the best player in the world.
"Messi will always be decisive. He's the best player in the world," Pochettino told Argentine newspaper Ole.
"Messi has the role today that can give Argentina the World Cup. He's the clear leader of this team and everyone understands that he's the leader, all the energy is focused on that."
The Parisian club parted ways with Pochettino in July after an 18-month stint where he won the 2020-21 French Cup and 2021-22 Ligue 1 title but failed to deliver in the Champions League.
Pochettino also managed Brazilian forward Neymar and France's Kylian Mbappe at PSG, but said Messi's ability makes him stand out.
"They're players who will always surprise you... You can understand the dimension of each one," Pochettino said. "In football terms, I highlight Messi's simplicity. The ability to make everything simple.
"It's very difficult to remember a training session in a year in which I've seen him make a technical mistake."
After their setback against Saudi Arabia and a crucial win over Mexico, Argentina will play their final group game against Poland on Wednesday.
