Puel managed Van Dijk during his year-long spell in charge of Southampton during the 2016-17 campaign and felt then that the centre-back was among the best, although a little rough around the edges.
Puel, who will come up against his former player when Leicester face Liverpool at Anfield on Wednesday night, believes playing in a top team has unlocked Van Dijk’s full potential.
“When I came in at Southampton he was, of course, a good player and I said at the time that for me he was the best defender in the world, but he was in comfort and had habits,” said Puel.
“He liked to defend deep on the pitch at the beginning and it was a shame he sometimes played too easy.
“At the beginning it was a little difficult to discuss with him and to change and evaluate, he got angry. But step by step he corrected things and improved his movement, cover and defending with cover and without risk.
“We know all the great teams like to have possession to play high up the pitch. The defenders need to learn to defend with a lot of space behind them. To play in great teams this is the aspect they need and he is now a modern defender at a very high level.
“At Liverpool, he has took another dimension. He is a fantastic player. My feeling about him doesn’t change with Liverpool. He is strong, powerful, fast, technical, he can play under pressure without a problem. It is fantastic.
“At Southampton he was the best defender in the world, but he confirmed it I think with Liverpool.”
Puel feels he may have another world-class defender under his charge in the shape of Harry Maguire.
The 25-year-old was reportedly the subject of interest from Manchester United during the last transfer window after impressing for England at the World Cup in Russia.
“I hope Harry can follow the same way,” said Puel. “Harry has also different attributes but a lot of aspects in his play to become a fantastic defender. He is a very good defender and can become one of the best in the world if he continues to improve.”