Chris Iwelumo has turned down a new contract offer from Colchester.
Iwelumo joined the Us from German side Alemannia in 2005
The 28-year-old striker, who has scored 37 goals in two seasons, has been discussing a new deal for the past few months but has failed to agree terms.
U's chief executive Marie Partner said: "The club has made every effort to put a competitive package on the table to Chris during the negotiations.
"However he has turned down the club's offer and we await to hear further news of his plans."