Barcelona man Song was sent off in the 40th minute of last Wednesday's game in Manaus after striking Croatia forward Mario Mandzukic in the back with his elbow.
Volker Finke's 10 men went on to lose the tie 4-0, confirming their exit from what has been a dismal World Cup for the African side.
Song received an automatic one-game ban for being shown a straight red card, ruling him out of Cameroon's final game of the tournament against Brazil on Monday.
And the 26-year-old will now be unavailable for two further international matches after FIFA opted to extend the suspension.
FIFA tweeted: "Decision of FIFA Disciplinary Committee sees Alex Song of Cameroon suspended for 3 matches."
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