The result hinged on a highly dubious penalty call, when United were leading through Javier Hernandez's second-half effort.
"Everyone was astounded," Ferguson told Sky Sports.
"The referee was so near. He was only eight yards away.
"Whether he ever gets a game again the assistant referee is not for me to decide.
"But it was an absolutely shocking decision. It costs you that.
"Two years ago when the linesman gave an offside goal for Chelsea it cost us the league."