Osorio discovered Sanchez as a 17-year-old in Colombia and helped develop the central defender during their time at Atletico Nacional.
His form in Medellin attracted interest from Europe's elite, with Catalan giants Barca keen to take him to Camp Nou – according to Osorio.
With plenty of options available to him, Sanchez sought the advice of his coach and Osorio was in no doubt he should snub Barca in favour of a switch to Ajax.
Sanchez followed his mentor's advice and after one season in Amsterdam joined Spurs for a reported £42 million.
Osorio is delighted to have seen the progression made by his former protege and believes his advice earlier in his career was proved right.
"I remember him calling me and asking if he should go to Ajax or Barcelona, who were also interested," he told Sky Sports.
"I just thought the best thing for him was to play football, and maybe in Barcelona he would not get playing time, he would be a sub.
"That is what he decided to do and then he went to Holland. He played a very good season and Tottenham decided to go for him.
"That's fantastic to see. When a player can have such an improving career in such a short period of time."