"The referee was bought by the fact Luiz rolled about," the Reds boss said. "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."
United’s final home game of the season is against Swansea next Sunday, when Sir Alex will demand more from his players before they lift the Barclays Premier League trophy.
"We don’t approach games in an easy way as there is an expectation all the time here," he added. "Maybe this will waken the players up."