De Bruyne is leaving City at the end of June when his current contract expires.
"Kevin has been just extraordinary,” Khaldoon told City's website.
“Obviously I have a subjective view. And my view is from the lens I see from the football I’ve lived over these years, obviously as chair, but also as a fan of this club.
"And Kev, what Kevin has given to this club. In my view, he is the greatest player to play for this club. I think his accomplishments speak for themselves.
“His accomplishments for the Club in terms of trophies. In terms of that tally, number of Premier Leagues, the Champions League, FA Cups, Community Shields, Carabao Cups. I mean, it’s an unbelievable tally, the highest of any player that’s ever played for this club."
A City leader
Khaldoon also said of De Bruyne: “His personal achievements, twice PFA Player of the Year. He’s been a captain. He’s been a leader. He’s been a team-mate. He’s been everything you’d hope from your most important player.
“His influence on everyone, from the academy to the communities of fans, not just of the club of Manchester City, but of football. All over the world, is unquestionable.
“So, Kevin, he really transcends this team and I’m so proud of what he’s accomplished. It’s one of the best decisions we ever took. The day we took the decision to invest in Kevin and bring him from Wolfsburg. I remember some people thought we overpaid.”