The newly-installed captain was sent off for a late lunge on Rudi Skacel in the club's 2-0 defeat to Hearts.
Riordan's dismissal pushed him through the SFA's disciplinary points banner, meaning he will miss the club's visit to Ibrox tonight and the home match this Saturday against Motherwell.
Embattled Aberdeen manager Mark McGhee believes he can still turn the club's fortunes around despite his Dons side suffering another loss last night.
Inverness' 2-1 victory at Pittodrie meant Aberdeen have only picked up four points from their last thirty and leaves them perilously close to the relegation zone.
McGhee was defiant after the match, saying: "As far as I'm concerned, we have training at 10am and unless I get a phonecall before then, I'm happy to continue. I am determined as ever to do well at Aberdeen."
The club's board is expected to consider McGhee's position in the next 24 hours.
Keven Mealamu's autumn tour with New Zealand is over after he was given a four-week ban for head-butting England's Lewis Moody on Saturday.
The hooker will be absent from the Kiwi side that will play Scotland this weekend. Mealamu, however, escaped an eight-week ban due to his "exemplary disciplinary record".
Murray up and running
Andy Murray begins his Paris Masters campaign this lunchtime, playing Argentina's David Nalbandian in the French capital.
Murray is looking to bounce back from a disappointing defence of his Valencia crown last week, where he lost in the third round to Juan Monaco.