LONDON -- Tottenham Hotspur manager Mauricio Pochettino has urged supporters to stay calm and trust chairman Daniel Levy over the future of Toby Alderweireld.

Alderweireld's £55,000-a-week contract is due to expire next summer and a source has told ESPN FC that he has rejected at least one offer of a new deal.

Spurs have the option of extending Alderweireld's contract until 2020, but doing so would activate a release clause allowing him to leave for £25 million during a two-week window in the summer of 2019.

They are determined not to reach that point, but Virgil van Dijk's £75m move from Southampton to Liverpool has highlighted the value of centre-backs and Alderweireld, 29 in March, knows he could potentially triple his wages by leaving.

But Pochettino said: "This is a message for our fans and for everyone: he still has two-and-half years of contract.

"[Lionel] Messi had six months left on his contract. Messi! Nothing is happening. If something happens, the club is going to communicate it. But I don't understand all these things when the players are all under contract.

"Daniel Levy said to me: 'Don't worry gaffer. It's two-and-half years.'"

Toby Alderweireld has yet to sign a new Spurs deal. TF-Images/TF-Images via Getty Images

Asked about the one-year option in Alderweireld's deal, Pochettino, who is not involved directly involved in contract negotiations, repeated: "Daniel Levy said to me: 'Don't worry, it's two years and a half.'"

Alderweireld and Erik Lamela, who has missed 13 months through injury, are the only senior players in Pochettino's squad who have not signed new deals in the past 18 months.

"It's not about saying the club needs to do this and this," Pochettino added. "Hey! Calm! Be calm, our fans. Because Daniel is very good. He has managed the club for 17 or 18 years.

"Look at how Tottenham was 18 years ago and how it is today. I think full credit to Daniel Levy and let Daniel work. It is important the fans trust in Daniel."

Alderweireld's importance to Spurs has been highlighted by his absence with a hamstring injury since the Champions League win over Real Madrid on Nov. 1.

Without the Belgium international, Spurs have kept just four clean sheets in 13 matches and conceded from corners in four of their last six league games.

Pochettino said: "We have been talking in the last few weeks [about the problem] and trying to improve.

"We made a mistake at Manchester City [when Ilkay Gundogan scored] and the small details can change the game.

"In the last two weeks, we were very focused on trying to improve our set-up and our mentality and be more aggressive.

"More commitment, more aggression in this type of situation because it can change the game.

"It's more about mentality. It's a collective mentality. We need to be more focused. In the last few games, we were better but it's a thing we need to improve."