Claude Puel says Virgil van Dijk's rise into contention for th mantle of world's best defender began under his tutelage at Southampton.
In the year since moving to Anfield, the Dutchman's reputation has soared following a run to the Champions League final last campaign and a push to the top of the Premier League table this season.
Many, including Puel, have earmarked van Dijk as the best centre-back in the world, but Puel says that evolution started well before the defender moved to Merseyside.
“When I came in at Southampton, Virgil was a good player but he was too comfortable," Puel said ahead of Leicester's clash with Liverpool on Wednesday.
“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 make cover and defend often one against one and remain compact.
“So we worked with different moves and examples of international teams to look at the defenders and the different aspects of a modern defender.
“He was angry at the beginning but, step by step, he corrected things and improved. He took another dimension. But Virgil has had always a big character and strong personality. At the beginning, sometimes it was difficult between both of us, but step by step I think he understood. He became a modern defender in this time and performed game after game.
“When one time he came back from his national team, I had watched his game and said it was perfect — his movement and cover. He had just a little smile and after this time he has had fantastic consistency, quality and performances.
“He listened in the end and is a fantastic player and competitor. He is strong, powerful, fast, technical and he can play under pressure without a problem.”
Van Dijk could miss Wednesday's fixture, however, as he has been battling an illness in the run up the match, but it appears he should be ready in time to feature.
With Manchester City's slip-up against Newcastle on Tuesday, Liverpool can extend their lead atop the Premier League to seven points.
If the Dutch defender does play, Puel expects it to be a tough test for his side, although he backed his own star defender, Harry Maguire, to provide a bit of frustration for Liverpool's attack as well.
“I said at Southampton Virgil was the best defender in the world. But he confirmed it with Liverpool," Puel said.
"I hope Harry can follow the same way. 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.”