Argentina manager Lionel Scaloni heaped praise on teenager Franco Mastantuono on Monday ahead of the River Plate midfielder's expected move to Real Madrid.

The Spanish club has reportedly agreed to a deal worth 45 million U.S. dollars for the 17-year-old, who made his international debut in Argentina's 1-0 win over Chile in Santiago last Thursday.

"Going to Real Madrid is a huge thing," Scaloni told a news conference on the eve of Argentina's home World Cup qualifier against Colombia.

"We're talking about the best or one of the best clubs in the world. It's a huge step for him and obviously he's still only 17."

Mastantuono has been a revelation for River Plate this year with seven goals and four assists in 19 games across all competitions.

But Scaloni warned of placing unrealistic expectations on the elegant left-footed playmaker.

"We need everyone around him to remember that he's only 17," Scaloni said. "We all have to help to make him better. I'm happy that this is happening because it means that big clubs are looking at Argentine football."

Meanwhile, Scaloni confirmed that captain Lionel Messi would start in Tuesday's clash at Estadio Monumental in Buenos Aires.

The 37-year-old began Thursday's clash on the bench as Scaloni rested key players in the knowledge that a World Cup place is already assured.

"Leo will start. We have no doubts, and we hope the fans enjoy him and the team," the 47-year-old head coach said.

Argentina leads the 10-team South American group with 34 points, 13 ahead of sixth-placed Colombia with three qualifiers remaining. The top six teams will earn direct entry to football's showpiece tournament in the United States, Mexico and Canada next year.