Tottenham Hotspur, in some way, are something of a paradox. Considered one of the most exciting, exhilarating sides in the Premier League under Mauricio Pochettino, their real strength can be found at the back, where they conceded fewer goals than any other team in the division last season.

Indeed, for all the brilliance of Dele Alli and Real Madrid transfer target Harry Kane,it’s Spurs’ defenders who provided the basis for their best league campaign in a generation.

Serge Aurier, Kieran Trippier, Danny Rose and Ben Davies are some of the best full-backs in England, while Hugo Lloris is considered one of the most reliable goalkeepers. As is the case in most teams, though, it’s the centre-back pairing that provides the lynchpin.

Toby Alderweireld and Jan Vertonghen have formed the most formidable centre-back pairing over the past two seasons, with one getting the best out of the other. Not since the days of Rio Ferdinand and Nemanja Vidić has the Premier League seen a defensive pairing like it. They are the crux of Spurs’ recent success.

Pochettino has been quick to sign his most important players to new contracts of late, with Vertonghen agreeing a new deal in December 2016. Alderweireld, however, remains on the same contract he joined Spurs on in July 2015. Talks between the two parties were reported to have started in the summer, but nothing has been signed still.

His current contract expires in 2019 and a clause states that, if a year-long extension is triggered, the player can leave for a fee of £25million up to 14 days prior to the 2019 summer transfer deadline.

Of course, there are no shortage of teams looking for new centre-backs and Alderweireld would command a place at most teams anywhere in Europe.

He has been left out of the squad for the game against Juventus, and while that is likely to be as he recovers from injury, it could be due to his future being up in the air.

Not that Pochettino seems particularly concerned.

“This is a message for our fans and for everyone: Toby still has two-and-a-half years of contract,” Pochettino said early this year.

“Messi was six months left on his contract. Messi! If something happens [on Alderweireld], the club is going to communicate. But I don’t understand all these things when the players are all under contract.”

In the past, Pochettino might have had more reason for concern. Spurs were, not so long ago, a selling club, with Michael Carrick, Dimitar Berbatov, Luka Modrić and Gareth Bale all sold when bigger clubs with more money came calling. Daniel Levy earned himself a reputation as a master negotiator, but he almost always came to an arrangement that saw his club’s prize assets leave.

Now, the dynamic has changed. Spurs have qualified for the Champions League in back-to-back seasons and are moving into their new, state-of-the-art stadium for the start of the 2018/19 season.

They are no longer looking upwards at the big boys, they are one of the big boys.

This allows them to keep hold of their best players, such as Kane, Alli and as Pochettino will hope, Alderweireld.

But for all that Spurs have made undeniable progress in keeping hold of their best players, the hypothetical loss of Alderweireld would be one that hits hard. The Belgian is arguably their most important player – and Spurs have missed him when he's been injured this season.

He made more blocks than any other Spurs player last season, also averaging more clearances than any other player besides Vertonghen. Alderweireld’s numbers make for impressive reading but the real proof in his play can be found in the qualitative. He is stylistically crucial to Spurs and the team Pochettino has put together.

It’s for this reason Spurs must do everything possible to keep Alderweireld at the club. Levy still operates a tight wage structure at the club but, for the sake of the progress they have made of late, they must push it to the limits to keep Alderweireld happy. He’s worth it.