An arbitrator has upheld the two-game ban, which was originally handed down July 23.
Mitchell appealed the decision and has remained in the lineup waiting for the case to be heard.
The incident occurred in a July 22 game between Edmonton and B.C., when Mtchell violently pulled on the arm of Edmonton offensive lineman Simeon Rottier.
Rottier left the game and although he returned to the sideline in the second half, he didn't resume playing.
The suspension is significant by CFL standards because it's the longest issued by commissioner Mark Cohon.
"I accept the decision of the arbitrator and I am grateful for having had the opportunity to go through the process of an appeal," Mitchell said in a statement.
No penalty was called on the play.
Mitchell will miss the Lions next two games — Sunday at home against Saskatchewan and Aug. 24 at Winnipeg.
"We welcome this decision and will continue to work with our players and their association to safeguard player health and safety," Cohon said in a statement.