The Real Madrid legend has heaped praise on the Blancos centre-back, as well as claiming Iker Casillas will leave the Santiago Bernabeu if he remains on the bench
The 45-year-old was himself a mainstay of the Galacticos defence for over a decade, and says the young Frenchman is now unrivalled in his position.
"There is no central defender in the world like Varane," Hierro told Radio Marca.
"For his age, his understanding of the game is amazing. He has the maturity of somebody who has been playing for 20 years."
Hierro also insisted that his former team-mate Iker Casillas will not be content with playing second fiddle to Diego Lopez in the Madrid goal.
"Anyone who thinks Iker will be happy on the bench is wrong," Hierro said. "He needs to be loved and the club should declare their faith in him publicly."
Hierro, who was capped 89 times by la Roja during his stellar playing career, spent 14 years at the Santiago Bernabeu.