Franco Mastantuono's transfer to Real Madrid came too soon, while the 17-year-old was still developing and pivotal to River Plate's future, said coach Marcelo Gallardo ahead of the Argentine team's Club World Cup match against Monterrey.

Gallardo acknowledged Mastantuono's departure will leave a void in his squad after the Spanish giants completed a deal worth around $45 million with River for the teenager earlier this month.

For the Argentine manager, the midfielder still needed more time to grow at the club, but he acknowledged the early transfer as an understandable part of modern football.

"It's natural, we train players for the world. Everything is happening earlier, young players are leaving faster, and I understand that those are the rules of the game," Gallardo told ESPN on Friday.

"Our sporting project for the year was with him. We have to readjust, because there are players who, by their nature, are difficult to replace.

"We knew that Mastantuono was going to leave at some point, but fans don't enjoy it that way. The market dictates the timing."

Gallardo said he's urging Mastantuono to stay focused on the tournament despite the noise around his move.

"All I want is for him to play naturally, to try to forget about everything that's going on, which is very difficult," he said.

"I don't talk to him about where he's going to live or anything like that. I want him to play, which is what he knows how to do."

River began their Club World Cup campaign with a 3-1 win over Japan's Urawa Red Diamonds, a result Gallardo described as key to easing early nerves.

"We are happy to be able to be in a competition like this, a new one," he said. "I'm excited about how it's going, it was essential to start with a win and get over the nerves.

"Now we're preparing for the match in Monterrey, which is a different level of difficulty."

Following Saturday's game against the Mexican team in Pasadena, River will face Champions League runners-up Inter Milan on Wednesday. REUTERS

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