The Saints' defender worked with the Real Madrid superstar in their early careers back at Sporting Lisbon in the youth team, before Ronaldo moved to Manchester United and took the Premier League by storm.
The former Crystal Palace defender believes that he sees some of the qualities in Ramirez which Ronaldo also possesses.
Fonte told reporters: “Cristiano was 16 and I was 17. He was already a special talent - I used to kick him in training.
"He is an unbelievable player and when you play against players like him you can only improve.
“In terms of quality, Gaston is right up there with the best.
“His technique, his control, his use of the ball and his understanding of the game is different to anyone else in the team. He gives us something else.
“He is a different type of player to Ronaldo - he is a number 10 and Ronaldo is all about pace - but, creativity-wise, Gaston is up there.
|SAINTS CLAIM SIX-POINTER|
|9/1||Southampton are 9/1 with Paddy Power to beat Reading 2-0 today|
“He is only 21 and knows he has to keep working hard to improve, but he will be a great player in this league - just like Ronaldo was.”
Fonte explained: “I know how Cristiano worked. He was young when I played with him but he wanted to be the best in the world.
“I have seen it with my own eyes - him doing press-ups in the shower. I know he trained hard to get where he is.
“I am fortunate to have worked with him and seeing how far he has come gives me a lot of inspiration.”
Southampton host relegation strugglers Reading on Saturday afternoon, in a game that pundits are already labelling a 'six-pointer'.