The 22-year-old is out of contract and is unhappy at the terms of the new deal offered to him by the club, and seems likely to look for another employer in the summer.
Rangers are reported to be long-term admirers of the player, while their Old Firm rivals Celtic are also interested in signing him.
And the names of Everton, Hamburg, Bochum and Sporting Lisbon have been added to the list in recent days.
Perhaps this should be taken as a hint that Caldwell, who has looked to be Jonathan Woodgate’s best partner so far, is worth more than another one-year deal.