The Saints are in search of a central midfielder, with Joey Veerman of Heerenveen also on their list.
And their interest in 21-year-old Brest man Diallo has grown with further talks held today.
Gregory Lorenzi, the sporting director of Brest, confided in recent hours that Southampton have offered over €14m for Diallo.
Brest are not completely satisfied by the offer, despite the guarantee of added bonuses, but the clubs are moving closer to an agreement.
Diallo, a former French youth international, has started in all five of Brest’s Ligue 1 matches this season.
RMC Sport reports that Southampton have now had a €15m bid for Diallo accepted.
— Loïc Tanzi (@Tanziloic) October 2, 2020
Diallo is now a Southampton player.
Just another quiet Sunday afternoon in the media department… 😰
— Southampton FC (@SouthamptonFC) October 4, 2020