Charlton manager Alan Pardew said Ambrose had to make way for potential loan signings at the club.
Pardew told Charlton's website: "Someone had to be sacrificed to give us the financial room to bring one or two in, and Darren was the option I've taken."
Ambrose has made 116 appearances for the Addicks, scoring 16 goals, but missed the start of this season after undergoing a hip operation in the summer.
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