United full-back Rafael was handed his marching orders in the closing stages at Old Trafford for kicking out at his fellow Brazilian.
However, Ferguson has insisted that his defender was acting in retaliation.
"The referee was bought by the fact Luiz rolled about," Ferguson told MUTV. "He actually elbowed Rafael twice but you know what happens when a player retaliates: he's always punished more.
"Luiz made it look worse. I don't think the referee saw it, actually, and he was convinced by Luiz's reaction."
Rafael will now miss the last two games of the current season as well as the first match of the new campaign.