Landajo planted his foot into a ruck repeatedly in full view of referee Wayne Barnes, enraging Wallabies back Adam Ashley-Cooper, but received only a penalty for a tackle infringement and a caution despite the incident being scrutinised by the television match official.
The citing commissioner later deemed the incident had met the red card threshold for foul play and it was referred to a hearing.
"This was a reckless attempt by Landajo to free up the ball in the back of the ruck, resulting in him making contact with his boot on the hands of two Australian players," judicial officer Nigel Hampton said in a media release on Monday.
"This was a lower end offence and, given the early guilty plea, Landajo's contrition and his good playing record, appropriately could be dealt with by a one week suspension."
Argentina finished bottom of the table in the four-nation Rugby Championship, which was won by New Zealand for a second successive year.