The 22-year-old clashed with Dons striker Christian Ramirez and video footage appeared to show the Easter Road defender, who scored the winner with a 64th minute header, catching the forward in the groin with his boot.
Referee Alan Muir didn’t take any action at the time but the Scottish FA issued a notice of complaint on Christmas Eve, with Porteous accused of violent conduct.
A fast-track tribunal hearing was pencilled in for Thursday December 30 but cancelled after the player admitted the charge on Wednesday December 29.
Porteous incurred a two-match ban for the incident with Ramirez but his punishment is increased to three games as per the Judicial Panel Protocol which states: “Where a player is reported for a sending-off offence, and that player has also been determined by a tribunal to have committed an additional sending-off offence in the same match, or has previously been reported for a sending-off offence in the same competition in a season, an additional suspension of one match for each previous sending-off offence will be applied.”
The Scotland Under-21 internationalist received a straight red card in the 2-1 defeat by Rangers on October 3, with Hibs unsuccessfully appealing the decision.
Porteous has also accumulated six cautions in Scottish Premiership matches this term.
The defender will miss the games away to Celtic on Monday January 17, at home to Cove Rangers on Thursday January 20, and away to Motherwell on Wednesday January 26.