Bristol City captain Liam Fontaine's appeal against his dismissal in Tuesday's 2-0 defeat by Watford has been rejected.
Referee Oliver Langford brandished a straight red card after the defender floored Jonathan Hogg with a high lunge.
But manager Derek McInnes felt the decision was unjust and the club decided to appeal to the Football Association.
"I don't think there was any malice or intent there, it wasn't a reckless tackle," said McInnes after the game.
But the sending-off has been upheld by the FA and Fontaine must now serve a three-match suspension.
He will miss the fixtures against Middlesbrough, Derby County and Nottingham Forest, and is eligible to return for Easter Monday's home clash with Coventry City.