Alcaraz, who is only 18 years old, burst into the world's top 10 earlier this month after a spectacular win at the Miami Open was followed by a triumph at the Barcelona Open.
Now, Ferrer has told the ATP Tour Insider magazine that he saw Alcarez's promise in a young Alcaraz when they played together a few years ago in Alicante.
"I was surprised by his ball speed, but more importantly, I couldn't hurt him with my flat ball," Ferrer recalls. "I could tell he was quick because he used his hands so skillfully. He had excellent footwork for his age and it was difficult to smash a home run against him.
“I’ve trained with a lot of young boys. But when a 14-year-old copes with your tempo like that and you can see his desire to beat you in a tie-break – while always being respectful – it’s because he has something special.”
“Comparing them would be a big burden for Carlos. He will be a player who has a chance to be the No. 1 in the world. He will have a lot of chances to win Grand Slams, but he has his whole career ahead of him.
“Nobody can overshadow Rafa because of everything he has been and continues to be. The good thing is that we can enjoy both of them.”
Meanwhile, Alcaraz's younger brother Jamie is also showing genuine promise on the court.