The 24-year-old will only return for the last round in a blow to their hopes of pushing into the finals-bound top eight.
Kemeny showed his athleticism in their tight 33-26 defeat, charging 30 metres to the tryline to open the scoring.
But he was cited for a tackle on Brumbies centre Len Iketau midway through the first half, although wasn't penalised at the time for the action.
The citing commissioner deemed the incident met the red card threshold for foul play.
The SANZAAR Foul Play Review Committee of chairman Michael Heron KC, Stefan Terblanche and John Langford assessed the case and ruled the tackle was illegal.
"With respect to sanction, the Foul Play Review Committee held the act of foul play was late and dangerous with direct and forceful contact made head-to-head," Heron said in a statement.
"Whilst the player attempted to pull out of a late tackle, he was always high and there was no applicable mitigation."
The committee deemed the action warranted a six-week ban, which was reduced to three due to Kemeny's record and guilty plea.
That means the Sydney-born flanker will miss Saturday's clash with the NSW Waratahs in Sydney, an away match against the Highlanders and their final home game of the season against the Western Force.
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