However, he insists the 17 year-old will need support in Madrid to fulfil his potential.
Scaloni said ahead of their World Cup qualifier against Colombia: "Going to Real Madrid is a huge thing. We are talking about the best club in the world, or perhaps one of the best. It's a huge step and we talked to him recently.
"With that determination, that mentality and that desire to learn, he will certainly do well. We need everyone around him to know, however, that we are talking about a seventeen year old. We must all help him improve even more.
"I am happy if it happens, because it will mean that big clubs look to Argentine football. I hope it happens to others as it has been with (Javier) Saviola, (Juan Roman) Riquelme and (Pablo) Aimar in the past. Obviously, losing them is not a good thing, but it is really nice to see them on the weekends in the best clubs in the world."
Real Madrid are now in advanced talks to sign Mastanuono for his €45m buyout clause, with the youngster to remain with River for the rest of the calendar year.