Bale's return to Spurs hasn't panned out in the way many had envisaged, with the Welshman struggling for starts in the side and suffering injury setbacks.
The majority of his limited appearances have come as a substitute and the 31-year-old has not hit the heights manager Jose Mourinho had expected.
The Daily Star says Los Blancos could find it extremely difficult to get Bale off their books as a result of disappointing displays coupled with restrictive Brexit laws.
Having not been registered as a La Liga player this season, Bale will return to the Spanish capital as a non-EU player. This would result in the 31-year-old occupying one of Madrid's three non-EU players permitted by La Liga in matchday squads, limiting the club's ability in the transfer market.
Toni Roca, director of the Sports Law Institute, told AS: “In France, Italy or Germany, to name a few major leagues, Bale is a non-EU member. And seeing his performance and wages, it seems difficult for any great [club] to bet on him.
“Right now, the only option that seems viable in the event of a transfer is return to the United Kingdom. Another legal alternative? Surely a contract termination, but that would also imply a very high cost. It is not easy at all."