Tottenham have exercised their option to extend Toby Alderweireld's contract until 2020, but could risk losing him for £25m in the summer.
Alderweireld's deal was due to expire at the end of the season, but after triggering this option Spurs have activated a clause in his contract which states he can leave for £25m this summer instead of on a free transfer.
Spurs would have to receive that £25m offer from another club 14 or more days before the end of the summer 2019 transfer window.
Speaking in December, Spurs boss Mauricio Pochettino said it was an "obvious" decision to trigger the extension in Alderweireld's contract.
Sky Sports News understands Alderweireld was available for £25m last summer but no club made an approach.
It is understood Spurs have never had a formal approach from any club to sign the defender since he joined from Atletico Madrid in 2015 for £11.5m.
Alderweireld was a target for Manchester United last summer but the two clubs were apart in their valuation for a deal, according to Sky sources.
The former Southampton defender has been a key player for Tottenham this season having made 24 appearances in all competitions, including 17 in the Premier League.