Reguilon joined Spurs in a deal worth £25 million during the summer and has made four appearances so far this season.
Spanish publication AS per Sport Witness report Madrid are currently coming to terms with the 'unstoppable' decline of club legend Marcelo.
The Brazilian has been fazed out by Zinedine Zidane, who prefers Ferland Mendy at left-back.
But senior members of the 'Los Blancos' hierarchy are fans of Reguilon and are aware he could be brought back for around £40 million next summer if Mendy and Marcelo's performances don't improve.
The 23-year-old spent last season on loan at Sevilla and helped them win the Europa League.
Both Marcelo and Mendy started as Madrid slumped to a shock 3-2 defeat against Shakhtar Donetsk in their opening Champions League game on Wednesday evening.
The 13-time European champions found themselves 3-0 down in the first half and Zidane took responsibility for the performance.
"I am responsible and since the first half was negative, I have not done something right," he told reporters per Goal.
"The first goal changed everything and [ultimately] cost us, but this [Champions League campaign] has just begun and we are not going to give up."
Despite the defeat, Zidane remains confident he is the one to turn the current La Liga champions around.
"I see myself capable of fixing this, that's what I'm going to try."
"The players are going to try, too. We are going to look for the solution and we're going to find it. Now we have to prepare for Saturday's game [away to Barcelona].
"It's a bad feeling [that we have after this result], of course.
"It ended up being a mix of everything. We made a mistake leading up to the first goal and afterwards the truth is that we were missing a bit of confidence, a bit of action, a bit of everything in the first half.
"I am happy for the players who reacted and changed in the second half, because they don't deserve such things. It was a bad game, a bad night. I'm the coach, I'm the one who needs to find a solution, and I'm not going to find it tonight."
Featured Image Credit: PA Images
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