The move would eclipse Brentford's previous record outlay, last year's €42.8m signing of Dango Ouattara from Bournemouth, and comes as the Bees prepare to lose England international Jordan Henderson to Chelsea.
Sangaré, 23, arrived at Lens last summer from Rapid Wien via an earlier spell at RB Salzburg, and made an immediate impact in his first season in Ligue 1, scoring three goals and adding four assists in 29 appearances as the club finished second behind Paris Saint-Germain, qualified for the Champions League and won the Coupe de France for the first time in the club's history.
His performances also earned him the Marc-Vivien Foé Award as Ligue 1's best African player and had previously attracted interest from both Liverpool and Manchester United.
The reported €48m fee would represent a club-record sale for Lens too, surpassing the €40m RB Leipzig paid for Lois Openda in 2023, and a huge profit on the roughly €8m they paid to sign Sangaré only a year ago. He was left out of Lens's Como Cup friendlies against Crystal Palace and Famalicão as talks over his future progressed, with Brentford now working through the final details before completing the deal.
Crystal Palace, managed by Sangaré's former Lens boss Pierre Sage, had also registered interest in the midfielder, but with Brentford's agreement in principle already reached, the Eagles would need a late intervention to prevent the move going through.
Sangaré, who has 16 caps for Mali, was already attracting attention before his move to France, having topped the Austrian Bundesliga for ball recoveries and duels won in 2024/25 and led the Conference League in both categories during the same campaign.
Brentford, under manager Keith Andrews, see the defensive midfielder as a direct like-for-like solution to fill the void left by Henderson's departure, with the club continuing a recruitment strategy built around signing players entering the prime years of their careers rather than the finished article.