Although Ajax are understood to have provisionally agreed a deal to sell De Jong to Barcelona next summer, Mauricio Pochettino is determined to hijack the move and sign the highly-rated youngster.
Despite his £45m offer earlier this week, Pochettino has been informed that the 21-year-old Dutch midfielder is not for sale.
De Jong, who made his debut for the Netherlands against Peru earlier this week, has said that he will not make a decision about his future until the end of the season.
He has also attracted interest from clubs such as Paris Saint-Germain, Manchester City, Roma and Borussia Dortmund after breaking into Ajax's first team last season.
As De Jong has previously said that he would like to play with Lionel Messi, Barcelona look to be the favourites to get his signature.