Conn. Gen. Stat. § 52-140: Set-off by defendant in suit by assignee.

In any action brought in his own name by the assignee of a chose in action not negotiable, the defendant, or any of the defendants, may set off, in the manner and to the extent provided in section 52-139, any mutual debt between him and the plaintiff or any of the plaintiffs, or between him and the assignors of such chose in action, or any of them.