Hazard, 26, injured his ankle during training while on international duty with Belgium and underwent surgery in England on 5 June.
Chelsea confirmed that the midfielder would be out of action at least until September. The new Premier League season kicks off on 12 August.
Cole said the news could be a blessing in disguise for the Blues as it reduces the chances of 12-time European champions Real Madrid launching a move for one of the Premier League's brightest talents.
"He is fantastic. He is one of the top players in the world," Cole told Goal.
"It is a shame he got this injury with Belgium but with the speculation that was coming, on a selfish point of view for Chelsea, it might mean that we can keep hold of him for another year.
"For me, he is the best player at the club. I think he is the best player in the league. I can't speak highly enough of him. He would be very expensive to replace. I don't know where you could go to replace him. Eden is a leader in the dressing room.
"He is also very well liked in the dressing room. People around the club like him and he appears to have settled very well. He is an established player and it is very important that the club keeps hold of him."
Hazard has been linked with a summer move to Real Madrid and said in an interview earlier this month he would have to consider his future at Chelsea if the Spanish giants made an offer for him.
Madrid are expected to make a big-name signing in the summer transfer window to further strengthen a squad that won the La Liga title, the Champions League and the Club World Cup.