Both saw red in the first half of Sunday's 3-0 defeat to the Blades at Ninian Park, with Bluebirds boss Dave Jones confirming straight after the game the club would appeal both dismissals. But they may also use Blackwell's quotes as evidence to support their case.
The United manager admitted "both red cards looked harsh to me" before going on to say "I honestly don't know why he (McCormack) was dismissed".
Both Gyepes and McCormack are facing three-match bans, and with only nine games remaining for Cardiff this season the suspensions could seriously damage their promotion hopes.
No date has yet been set for the appeal which will be held before the Football Association of Wales, but it is sure to take place before the club return to action against local rivals Swansea on April 5.