Liverpool accepted Brentford’s £18m ($24.2m) bid for goalkeeper Caoimhin Kelleher.
The 26-year-old Republic of Ireland international is in his final year at Anfield; his value was £20m last summer.
The final fee could reach £18m, factoring in performance-based add-ons.
Brentford has scheduled a medical for a Republic of Ireland international player on Monday.
Brentford has long tracked Kelleher, showing interest even before signing Flekken; however, Liverpool only considered selling him after acquiring Giorgi Mamardashvili from Valencia last summer.

Although other teams, such as Leeds and West Ham, have also been vying for 26-year-old Kelleher, Brentford, who enjoy a strong relationship with Liverpool after previous transfers, are in the running.
Mark Flekken’s move to Bayer Leverkusen can be finalized after the transfer is complete.
Leverkusen and Brentford have reached an agreement on a transfer fee of around £11m (€13m), including add-ons, for Dutch international Mark Flekken.
Reports from Germany suggest Flekken is about to have a medical at Leverkusen.
Flekken will join former Manchester United manager Erik ten Hag in Germany, pending the transfer’s finalization without complications.
Brentford has made a smart move, spending £1.5m to replace their 32-year-old (who turns 33 in 12 days) goalkeeper with a 26-year-old from Liverpool. This is thanks to Phil Giles and Lee Dykes.