Now 16, four years ago Lamela was on the brink of a controversial move to Barca, which also involved Nike and would have been worth £100,000-a-month to his family. But pressure from Argentine football authorities saw the deal fall through.
Lamela is set to join River's first team squad for the first time next week and said: "I cannot wait for January 5. This is a dream, but I'll take it easy. I've still not done anything. I really want to learn."
The young midfielder has been likened to Lionel Messi and admits the Barca star is his idol: "It's hard to be like Messi, but Lionel is my hero.
"I really want to show everyone that the talk about me is not a lie."