Hazard, who has helped the Blues win five major trophies since arriving in west London in 2012, was named PFA Player of the Year in 2014-15 and continues to lead by example for Maurizio Sarri's side.
And former England international Cole, who spent a year with the Belgian while at Lille in 2011-12, always felt Hazard's skill level would see him become a fan favourite at Stamford Bridge.
“I said when he signed that he would be the greatest player the club has ever had and I still stand by that. I still believe that,” Cole told the Daily Mirror .
“My team-mates and my colleagues have been amazing but Eden is the best player I've ever worked with.
“When you look at what he's done in the short space of time that he's been there. He's been an unbelievable player. I think he's the best player in the league and I think he's a top, top player and it's important the club keep hold of him.”
Cole’s praise for Hazard is even more remarkable considering who the 37-year-old played with during his seven-year stint at Stamford Bridge.
The former midfielder was a team-mate of the likes of John Terry, Ashley Cole, Frank Lampard, Didier Drogba at Chelsea, but ironically it is a player who has since moved to Chelsea, whom Cole considers to be the best he ever played with.
So impressed was the now Chelsea coach with Hazard, he even encouraged him to join the Blues in the summer of 2012.
“I played with him when I was at Lille and he was being courted by all the top clubs in Europe and Harry Redknapp was talking to me about him because Tottenham wanted him,” said Cole.
“Everyone wanted him - Man United, Man City and I just felt Chelsea was the right home for him.
“I told him if he wanted to win trophies which he has done and develop as a player. London is close to Belgium on the Eurostar, I felt it was the right fit and I knew the fans would love him.”
Hazard continues to be linked with a move away from Chelsea, with Real Madridreportedly keen to bring him to Santiago Bernabeu.
For now, though, his concentration is focused on firing the Blues back into the Champions League, with Sarri's side next in action against Huddersfield Town on Saturday.
