Alderweireld has been linked with Tottenham for a few seasons now. While his contract is owned by Atlético Madrid, he is on loan this season at Southampton where he has played very well. In recent comments to the media, Alderweireld stated that he would prefer to remain in the Premier League, and that getting the chance to play alongside his Belgium national teammate Jan Vertonghen would be peachy-keen:
I would like to play with Jan Vertonghen again, but a transfer will be arranged later, not now. Atlético will decide my future, but I would like to stay in the Premier League. That some of the big clubs show interest proves I'm doing well.
That interest comes from a number of Premier League clubs. Spurs are of course tracking him, and Manchester City are also reportedly interested in his signature. And then Southampton has a £6.8m purchase clause in their loan contract with Atlético, but the Telegraph suggests the Rojiblancos can buy out that clause for £1.5m if they think they can get a better deal for Toby from another club. And that's assuming they don't just decide to keep him in Spain. The price quoted to purchase him from Atlético is said to be around £10m. In the end it would depend on just how badly a club like Spurs or City want him, and if they're ready to screw over Soton to get their man.
Alderweireld and Vertonghen obviously have a lot of experience playing together. The irony is that, for Belgium, Vertongen plays mostly at left back, with Alderweireld at right back. At Spurs, they would most likely start in central defense, their preferred positions.
Alderweireld would be a nice signing for a club like Spurs, but a lot needs to happen before we begin to call this a thing. For now, I'm pretty skeptical that this will happen, though having a good player say they'd like to join your club is pretty swell.