Mitchell was cited under Law 10.4 (j) Lifting a player from the ground and dropping that player into the ground whilst that player's feet are still off the ground, such that the player's upper body comes into contact with the ground.
The incident occurred in the 52nd minute of the match and his case was heard by Judicial Officer Nigel Hampton QC, who found that Mitchell breached Law 10.4 (j).
"After reviewing all of the evidence I concluded that Lachlan Mitchell had lifted and dropped Simon Zebo when that player's feet were still off the ground causing Simon Zebo's upper body to come into contact with the ground," said Mr Hampton.
"I found that the incident was clearly at the lowest level for this offence. The penalty associated for the lower level breach of Law 10.4 (j) is a suspension of four matches.
"Because of the circumstances and Lachlan Mitchell's good on-field record I have determined that the maximum reduction to the sentence of 50% should be applied. Further to this I found that an additional discount to the suspension should be made as I believe a two match penalty would be disproportionate to the level and type of offence that has occurred.
"As such I have delivered a sanction of a one match suspension, which will be fulfilled following the Rebels next Super Rugby fixture on Friday, 12 July."