The Daily Mail says the 6ft 2in, 17-year-old only made his first-team debut in August but is powerful, quick and good in the air.
He joined River Plate two years ago and came through the ranks as a second striker.
But he has converted to left wing and likes to imitate the Real Madrid star he is compared to, saying: "Everybody wants to be like Messi, but Ronaldo is the one I like. I try to imitate him."
Inter Milan are already reported to have had a bid of up to £15m rejected for Ocampos while Bayern Munich have also made enquiries. Liverpool and Manchester United have been alerted to his ability but Chelsea are ready to outbid them.