Dunne accepts sending off.The U's won't be appealing Clinton Morrison's red card.
"While I don't think there was any contact by his elbow, and definitely no intent or malice, Clinton's arm was above his head and that made the contact."
He told the club's official website: "I have looked at the incident again on DVD and can understand why the referee made his decision.
At the time, it looked a harsh decision, but boss Joe Dunne won't be speaking to the Football League about appealing the decision.
His dismissal came at the end of the 2-1 defeat at Northampton on Tuesday night.