Derby County let Darren Bent join Championship rivals Burton Albion on loan in the January transfer window while Jason Shackell headed to Millwall.
Rangers could be in need of a new central defender at Ibrox.
Millwall looked set to compete with Leeds United for Aston Villa defender Tommy Elphick but the Lions are in talks with Derby County's Jason Shackell.
Jason Shackell is one of a number of senior players Derby County boss Gary Rowett wants to leave, and Millwall could take him off the Rams' hands.
Championship promotion hopefulls Derby County are shaking up their squad this month and have allegedly offered Chris Martin to Leeds United.
Derby County's Jason Shackell is set to miss the rest of the season after undergoing surgery on his back.
Derby County are set to take on Nottingham Forest in Gary Rowett's first match in charge.
Shackell has been one of the most consistent second tier defenders in recent seasons - not that Derby need him.
Jason Shackell had been a key member of the starting XI until September but his injury has allowed Alex Pearce to step up.
The Rams have several players back in full training as they prepare to welcome Leeds United to the iPro Stadium.
From 22-year-old captains to lower league veterans, the second tier is hardly lacking in centre-backs who belong at a higher level.
Neil Redfearn claims Burnley's Joey Barton, Derby County's Jason Shackell, QPR winger Matt Phillips and Stoke City ace Charlie Adam all wanted to join Leeds.
Derby County announced Jason Shackell will wear the number 14 shirt next season after he took part in his first training session back at the club.