Brentford have accepted a £4m offer from Sheffield United for centre-back John Egan, Sky Sports News understands.
The Blades have been interested in Egan for sometime and attempted to sign him in the January transfer window.
And the 25-year-old is set to return to Bramall Lane after being loaned to the Yorkshire club in 2012 while at Sunderland.
Egan, who has two caps for Republic of Ireland, played just one game for them however, and returned to the Stadium of Light, where he also failed to break into the first team.
He switched to Gillingham where he made 81 appearances for 2014 to 2016, before moving to Brentford where he played 63 times and was made club-captain at the start of last season.
Should they lose Egan, the Bees have lined up potential centre-back replacements, having already signed centre-half Ezri Konsa from Charlton to replace Andreas Bjelland.
Sheffield United have a pre-season friendly with Inter Milan to look forward to on July 24 before kicking off their Championship campaign against Swansea on August 4 live on Sky Sports.