The Ajax manager believes his side will struggle to fill the void left by the Denmark international should he complete a prospective move to Tottenham.
Ajax technical director Marc Overmars revealed that Spurs have opened talks with the Eredivisie power over the signing of the Denmark international -- who has long been tabbed to leave the club this transfer window -- earlier this week.
De Boer has paid tribute to the 21-year-old's attitude and admits it will be tough to replace the attacking midfielder should he seal a switch to White Hart Lane.
"We always got along together very well. Footballers who are good players and also ideal professionals, are ideal players for a coach," De Boer told De Telegraaf. "His departure is a huge blow for us, because Chris is terribly important for us.
"[Whether we can replace him] depends on which player we can buy or take over on loan. They won't be at the level of Eriksen, but close to it."