De Jong will be sold to the highest bidder at the end of this season.
Paris Saint-Germain are in pole position, after telling Ajax they will pay £67million.
But Madrid have made Eriksen a top summer target as they look to revamp an ageing squad, and Spurs have responded by contacting De Jong’s agent, Ali Dursun, and giving him guarantees that will match the current highest bid for his client.
Tottenham know they will have to spend bigger than ever before to replace the 26-year-old Danish international – with a move to their new £1billion stadium looming and manager Mauricio Pochettino wanted by Manchester United .
Their current transfer record is the £42million they paid Ajax for Davinson Sanchez in 2017.
But Tottenham would bank £100million-plus from the sale of Eriksen, who has told his Monaco-based Dutch agent Martin Schoots that he will only leave Spurs to join a top club in Spain.
He is coveted by Madrid — although arch-rivals Barcelona have also been tracking the playmaker, ironically another former Ajax starlet.
De Jong, 21, looked destined for Manchester City late last year, only for the Premier League champions to request that the deal for him was put on ice.
That enabled PSG to launch a charm offensive, and Dursun met with officials of the French champions in Amsterdam in December.
De Jong was devastated to miss out on the chance with Pep Guardiola at City, but was impressed when PSG put their money on the table with an offer than included a contract worth £100,000-a-week AFTER tax.
He currently earns less than £10,000-a-week in Holland.
While Barcelona and Italian champions Juventus are also big admirers of the Dutch international, Barca are currently unwilling to match the financial offer being made by PSG and De Jong ruled out Juve because he believes a move to England, Spain or France will suit him best.
Spurs are long-term admirers of the player and have been tracking his progress for the past 18 months.
As well as signing Eriksen and Sanchez, they have also recruited Jan Vertonghen from Ajax in recent years. Toby Alderweireld is another current Spurs star who came through the Amsterdam club’s productive youth system.
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De Jong looked to be out of their range when City and PSG entered the race for his signature, but chairman Daniel Levy has developed a strong working relationship with Ajax director of football Mark Overmars and knows the kind of financial commitment he will have to make.
The belief in Amsterdam is that PSG remain favourites to land De Jong at the end of the season, but until and agreement with Ajax and De Jong is sealed the player remains on the market.
It is clear that if Eriksen follows in the footsteps of Gareth Bale and Luka Modric, then Spurs will spend what it takes to get a world-class replacement.