Scottish champions Celtic are showing an interest in Magnus Okuonghae, Sky Sports understands.
A host of clubs are tracking the 26-year-old - who is set to leave League One Colchester United after his contract expired.
But a number of Championship clubs are also keen on securing his signature.
Sky Sports understands the likes of Blackburn, Bolton, Burnley, Charlton, Derby, Millwall and newly promoted Sheffield Wednesday are all keen.
Former Dagenham & Redbridge defender Okounghae has also been offered a new contract at the Weston Homes Community Stadium.
"We have been contacted by a few clubs and Magnus will be considering his options over the coming weeks," his agent Leon Callendar of Straight Ace Management told Sky Sports.