"However, taking into account mitigating factors including the player's admission of guilt, his remorse and the fact that the player had a good disciplinary record having not come under notice since 2012, the judicial committee reduced the suspension to three weeks."
Already reeling from skipper James Slipper's season-ending injury, it is another hammer blow to the Reds who sit second on the Australian conference but only have one win from four games.
Cooper will miss games against the Jaguares, Hurricanes and Brumbies before being available for selection against the Kings on April 15.
The mercurial pivot had already been flown home to Brisbane, suggesting the Reds were well prepared for the suspension.
Jake McIntyre is already a confirmed starter at No.10 for Cooper against the Jaguares with Henry Taefu as cover.
Former Brisbane NRL flyer Lachlan Maranta has been called into the Reds' squad.
Cooper flew home with Slipper, who ruptured an Achilles tendon in the Lions' romp at Ellis Park.