Alejandro Sabella's men are among the favourites to lift the trophy in Brazil, and begin their campaign with a Group F fixture against Bosnia-Herzegovina on Sunday.
However, while praising Argentina's considerable attacking threat, Ardiles - part of the 1978 World Cup-winning side - questioned the team's rear guard.
"Going forward, Argentina have the best team in the world right now with (Angel) Di Maria, (Sergio) Aguero, (Gonzalo) Higuain and (Lionel) Messi," he told Tottenham's official website.
"But the team is a little unbalanced and our defence could be our Achilles heel, so we will have to wait and see."
Despite his doubts about the Argentine defence, Ardiles feels they are among a number of leading contenders for the title.
"I would say Argentina will reach the semi-final at least," he added. "I believe the winner will be a team that has already won the World Cup, so I’m looking at Argentina, Brazil and Spain."
After their match with Bosnia-Herzegovina, Argentina will come up against Iran and Nigeria in their remaining group fixtures.
