The former Real Madrid defender is back in North London following an uneventful loan spell with Manchester United in the first half of the season, where he made 12 appearances across all tournaments.
Only four of those matches were Premier League starts, though, while he also featured from the first whistle just once in the Champions League, failing to come off the bench in the Red Devils' last three group matches.
With Luke Shaw and Diogo Dalot representing alternative left-back options - as well as the injured Tyrell Malacia - both clubs agreed to terminate Reguilon's loan spell earlier this month, and the Spaniard is back working with Ange Postecoglou's squad.
The 27-year-old's availability could potentially come in handy following Ben Davies's hamstring injury, which is set to rule the Welshman out for a few weeks, leaving Destiny Udogie with no recognised backup.
However, both Emerson Royal and Ryan Sessegnon are capable of filling in at left-back when need be, and according to L'Equipe, Reguilon is likely to leave the club again before the January window slams shut.
The report states that Brentford are close to reaching an agreement over the temporary signing of the defender from their London rivals, who have Reguilon under contract for another 18 months.
Brentford have been expected to bolster their left-back options this month following Rico Henry's serious knee injury, which he sustained in September, and the 26-year-old is not likely to play again this season.
Aaron Hickey is also expected to miss the remainder of January with a thigh injury, while Saman Ghoddos - who has been deployed as an emergency full-back over the winter period - is representing Iran at the Asian Cup.
The Bees are not thought to be putting all their eggs in one basket, though, with a separate report claiming that they have enquired over the availability of Marseille man and former Nottingham Forest loanee Renan Lodi.
While still on the books at Real Madrid, Reguilon won the Europa League on loan with Sevilla in the 2019-20 season, after which he left the Bernabeu for Tottenham in a £25.8m transfer.
The Spain international has two goals and nine assists to show from 67 games in a Spurs jersey but was loaned out to Atletico Madrid for the 2022-23 campaign, where he was also restricted to just 12 appearances due to fitness problems.
Reguilon was involved in Tottenham's pre-season preparations, but he made just one appearance in Spurs' summer friendlies, playing the first half of a 3-2 loss to West Ham United in July.