The former Aston Villa and England midfielder, who had started Town's two previous games, did not figure in the 0-0 draw at Cardiff on Saturday.
Manager Mick McCarthy revealed the 28-year-old had declined the chance to extend his contract until June.
"I understand that, I think he may have some other [long-term] offers. He's been great," said McCarthy.
Reo-Coker made eight league appearances for the Tractor Boys after joining the club last October.
He also appeared against his former club Aston Villa in the FA Cup earlier this month.
Nigel Reo-Coker has turned down the offer of an extended contract at Ipswich Town and left the club.