The Spaniard was regarded as one of the most exciting full-backs in Europe after helping Sevilla win the Europa League in the 2019-20 season during a loan spell from Real Madrid.
With Marcelo and Ferland Mendy blocking Reguilon's route into the Blancos' first team, Tottenham forked out £25.8m to sign him from Real in 2020, but he has largely flattered to deceive in North London.
Reguilon also failed to reignite his career on loan at Atletico Madrid last term, making just 12 appearances in all competitions and failing to bag a single goal or assist, although he was hampered by groin surgery and a digestive issue, which required hospital treatment.
The 26-year-old has been a part of Ange Postecoglou's pre-season squad, but he is only under contract in North London for another two years and faces competition from Destiny Udogie and Ben Davies out wide.
As a result, a summer exit is not beyond the realm of possibility, and according to journalist Fabrizio Romano, Real Sociedad possess a "genuine interest" in Reguilon.
However, the La Liga side's interest is at its earliest stages, and they are yet to enter advanced talks with Tottenham over a deal for the former Real Madrid youngster.
Nevertheless, Spurs would not be expected to turn down an appropriate bid for the Spain international, who has made 67 appearances for the Lilywhites since his arrival three years ago.
Reguilon has come up with two goals and nine assists for Tottenham in that time and has played six times for Spain since joining the club, but it has been nearly two years since his last appearance for La Roja.
On the back of their disappointing eighth-placed finish in the Premier League last term, Spurs have added to their ranks with the captures of Guglielmo Vicario, James Maddison and Manor Solomon, as well as converting Dejan Kulusevski's loan into a permanent deal.
However, the North London club have only sanctioned two departures, selling Harry Winks to Leicester City for £10m and letting Lucas Moura run down his contract.
At least one new centre-back should arrive at the Tottenham Hotspur Stadium before the window shuts, but Reguilon could be one of several outgoings in the coming weeks as Postecoglou trims his squad.
Hugo Lloris, Davinson Sanchez, Japhet Tanganga and Joe Rodon should all be allowed to leave for a suitable fee, while the futures of Ivan Perisic, Giovani Lo Celso, Pierre-Emile Hojbjerg, Bryan Gil and Tanguy Ndombele are also clouded in uncertainty.
All-time leading scorer Harry Kane remains the subject of interest from Bayern Munich, who are expected to meet with Daniel Levy on Monday in the hope of reaching an agreement after failing with their opening two bids for the England captain.
Amid the speculation surrounding a potential Bundesliga move, Kane netted in a 5-1 thrashing of Lion City Sailors in Singapore on Wednesday, and Spurs will host Shakhtar Donetsk in their penultimate summer friendly next Sunday.