Tottenham have had their opening contract offer to Japhet Tanganga knocked back, Football Insider understands.
The north Londoners are working on a deal to keep the 20-year-old centre-back, whose current agreement ends next June.
A Tottenham source has told Football Insider the club are working on trying to keep hold of Tanganga and have offered him an extension on improved terms.
Tanganga has rejected the first offer, although Spurs are expected to return to the negotiating table with a new one.
The club are hopeful they can tie down the rising star, who has graduated from their youth ranks after first joining the club aged 11.
Along with central midfielder Oliver Skipp, 19, and centre-forward Troy Parrott, 17, Tanganga is regarded by the Spurs coaching staff as one of three academy products capable of establishing themselves in the first team in the future.
The young defender was handed his debut by Mauricio Pochettino earlier this season with a 66-minute run-out in the League Cup defeat to Colchester United.
Spurs humiliatingly lost that match on penalties after it finished goalless at full-time, but Tanganga made a stronger impression than fellow debutant Parrott.
Skipp has gained the most first team experience of the three rising stars, but Tanganga has the advantage of playing in a position that the club are likely to need to fill in the next year or two.
Of the three most senior centre-backs at the club – Jan Vertonghen, Toby Alderweireld and Davinson Sanchez – the former two are out of contract next summer.