Mauricio Pochettino has confirmed Tottenham will activate a one-year extension clause in Toby Alderweireld's contract, as they recently did with Jan Vertonghen.
That move prevents Alderweireld, who has been linked with Manchester United and Barcelona, from leaving for free in 2019 and keeps him at the club until 2020, but it also activates a release clause which makes the centre-back available for £25 million in the summer.
Asked whether Spurs intend to activate the clause, Pochettino told a news conference: "Yes, for sure, it's obvious. The same situation as Jan [Vertonghen]."
Pochettino said Spurs will need to sell players in January before they can think about signing anyone and added it will be difficult to recruit.
They did not bring in a single signing during the summer transfer window and need to boost their quota of homegrown players, having been forced to leave three foreign players out of their squad for the Champions League group stage.
"We're always open [to signing players in January] but it's going to be difficult -- maybe not impossible but difficult," Pochettino said.
"Maybe every day we talk [with chairman Daniel Levy and chief scout Steve Hitchen] but it depends on if players are going to leave, and to have space to sign players.
"It depends on players out and then we're going to see if we can add some quality to help the team. But I think it's not going to be easy to add players in January. For sure it's going to be tough to add.
"Until the market is open it's difficult to talk because now we have a lot of games to play. But for sure in January when the market is going to be open, that's the moment when we're going to talk with different players -- players that maybe come to talk with us because they want to leave or they want to play more.
"It's a normal period where we need to be open and careful about our decisions."