Sky Sports understands Millwall are in talks to sign former Brentford defender Karleigh Osborne.
Osborne is available on a free transfer after seeing out his contract at Brentford earlier this summer.
The 24-year-old is thought to have turned down a new deal at Griffin Park as he wanted to play at a higher level.
Osborne came through the youth ranks at Brentford and has established himself as one of the best defenders outside the top two leagues in England.
A number of clubs are thought to have expressed an interest in Osborne, but Millwall are hoping to win the race for the central defender's signature.
Lions boss Kenny Jackett is in the market for defensive reinforcements and he hopes to tie up a deal for Osborne.