The Spanish left-back returned to Hotspur Way earlier this month following a short stint at Manchester United, where he made 12 appearances in all tournaments under Erik ten Hag.
Reguilon only made the first XI on four occasions in the Premier League, though, having faced stiff competition from Luke Shaw and Diogo Dalot while on the books at Old Trafford.
As a result, Tottenham terminated Reguilon's Man United loan spell six months early, but the 27-year-old currently does not feature in the plans of first-team boss Ange Postecoglou, who has made Destiny Udogie his first-choice left-back.
Udogie is short of natural cover due to Ben Davies's recent hamstring injury, which will keep the Welshman out for several weeks, but Emerson Royal is capable of playing on the left-hand side if required, meaning Spurs are happy to part ways with Reguilon.
It was reported over the weekend that Brentford were on the cusp of signing Reguilon on loan for the rest of the campaign, and according to The Athletic, a deal is indeed close to being finalised.
The report states that Reguilon has successfully completed his medical with Thomas Frank's side, and the Spaniard is expected to sign on the dotted line at Brentford's training ground this afternoon.
Spurs chairman Daniel Levy is understood to have played a prominent role in negotiations, and Tottenham have agreed to fork out a large chunk of Reguilon's wages during his loan spell.
Confirmation of Reguilon's move will mark the end of a sustained Brentford effort to bring the defender to the club, with the Bees reportedly touching base over his situation back in November.
Frank's side have now jumped through several hoops to bring Reguilon to the Gtech Community Stadium, and the ex-Real Madrid man is also believed to have been impressed with Brentford's sales pitch.
There is a strong chance that Reguilon will instantly become Brentford's first-choice left-back, as Rico Henry will miss the rest of the season with a knee injury, while Aaron Hickey is dealing with a thigh problem.
Frank has often shoe-horned Saman Ghoddos into a full-back role during Brentford's injury crisis, but the 30-year-old is also unavailable for the time being, having been called up to represent Iran at the Africa Cup of Nations.
Reguilon joined Tottenham for £25.7m in 2020 after becoming a Europa League champion with Sevilla, and the Spain international has registered two goals and six assists in 67 matches for the Lilywhites across all tournaments.
The 27-year-old fell out of favour under Antonio Conte, though, and he spent the 2022-23 season on loan with Atletico Madrid, but he played just 12 times for the club due to various fitness problems.
Tottenham still have Reguilon under contract for another 18 months, and his loan to Brentford will reportedly not include an option or obligation for a permanent deal.