Skysports.com understands Marc Tierney has turned down a new deal at Colchester.
Colchester have been locked in talks with Tierney over a new deal for the last few months, but the full-back has so far rebuffed their overtures.
Tierney has just over a year to run on his current deal and the news is sure to alert a number of clubs to his possible availability.
The 24-year-old has impressed this season, putting in a number of eye-catching performances for the League One hopefuls.
Scouts from Championship sides have been keeping tabs on Tierney and are monitoring his situation at the Weston Homes Community Stadium.
Colchester would be loath to lose Tierney, but could be forced to cash-in on him if he fails to agree a new deal.