Mauricio Pochettino leaving for Real Madrid, rather than Manchester United, is Tottenham's biggest fear

Tottenham Hotspur believe Real Madrid pose a bigger threat than Manchester United in their fight to hold on to manager Mauricio Pochettino.

And, as they battle to keep Pochettino, Spurs have taken a major gamble on the future of Toby Aldeweireld by deciding to extend his contract for a further year, despite a clause that states the defender can leave for £25million in the summer until 14 days before the transfer deadline.

United passed up the opportunity to sign Aldreweireld ahead of this season, but have made Pochettino their number one target to succeed Jose Mourinho as their next permanent manager.

The Old Trafford club are prepared to pay a world record compensation fee to try to tempt Spurs and are hopeful they could convince Pochettino to take on the biggest job in English football.

But sources close to the club claim Tottenham believe Real are a bigger threat to their hopes of keeping Pochettino if the La Liga giants choose to make another managerial change at the end of the season.

While there is a recognition that United would be an attractive proposition, Tottenham insiders feel Pochettino would be torn over quitting to immediately join another English club and whether or not it would be the right move at the right time.

But there has long been a fear around Spurs that Real and the opportunity to return to Spain would be difficult for Pochettino to resist, and there is now the added concern that United’s interest could force Real’s hand.

Tottenham’s recent form, which has seen them storm into the Premier League title race with successive 6-2 and 5-0 victories, has also further enhanced Pochettino’s reputation around Europe.

Real appointed Santiago Solari as the club’s permanent head coach in November, following the sacking of Julen Lopetegui, who had only lasted four-and-a-half months as Zinedine Zidane’s successor.

But shock defeats to Elbar in La Liga, in which Real currently occupy fourth place in the table, and CSKA Moscow in the Champions League, in which they have drawn Ajax, mean Real could reconsider their managerial situation again if they do not end the season with a major trophy.

Tottenham chairman Daniel Levy will fight hard to keep Pochettino by telling him he will not get the control he enjoys at Spurs elsewhere and is seeking outside investment to try to boost his summer transfer kitty.

There is also money to spend in the forthcoming transfer window, despite Pochettino last week joking that his pockets were empty.

Tottenham are not expected to be among the busiest clubs during January, but sources have told Telegraph Sport that there are funds available for the right player.

And Pochettino’s confirmation that Spurs might have to sell players to make room in his squad for any new arrivals may encourage January offers for Alderweireld.

Aldreweireld had been about to enter the final six months of his contract, but Pochettino revealed that, just as they did with Jan Vertonghen, Tottenham will take up their option of a 12-month extension.

But, unlike Vertonghen, Alderweireld’s extension includes a clause that allows him to leave for just £25m next summer until two weeks before the window closes.

Asked whether Tottenham will extend Alderweireld’s contract, Pochettino said: “Yes, for sure. It’s obvious. The same situation as Jan (Vertonghen).”

Confirming Spurs may need to offload players next month, Pochettino added: “We’re always open (to signing players in January), but it's going to be difficult - maybe not impossible but difficult.

“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.”

Following the thrashings of Everton and Bournemouth, Tottenham are second in the table, six points behind leaders Liverpool, ahead of Saturday’s visit of Wolverhampton Wanderers to Wembley, which Dele Alli has told Pochettino he will be ready for.

Pochettino has described every game as “a party” for Liverpool at Anfield and admitted that moving to their new stadium would be a boost for Spurs after a 45,154 Wembley attendance against Bournemouth.

“We cannot ask more from our fans, they are doing a fantastic job,” he said. “The circumstances of that period in the club, we need to be strong and we cannot complain about all that happened.

“That is why when I was asked before 'do you want to move?' I said 'of course, as soon as possible' because it's going to be a massive boost for the team. It's going to be a place where the fans can help the team to achieve more. There is no doubt. I am so happy with Wembley, but tomorrow if the new stadium is ready we are going to move to our new house.”