Skysports.com understands Millwall are facing a fight to keep hold of Danny Shittu.
Shittu's short-term deal with the Lions expires next month and a number of clubs are waiting in the wings to sign the experienced defender.
The Nigeria international has impressed at the Den since arriving in October after leaving Bolton in September
Millwall are keen to extend Shittu's stay at the club, but could lose the 30-year-old on a free transfer when the transfer window reopens.
Championship rivals Cardiff, Middlesbrough and Burnley are all thought to be interested in Shittu, along with an unnamed club in Germany and Greek side PAOK.