Ferguson also rates Bayern Munich as a threat.
"Bayern have always had capable and confident teams," the United boss, who has won Europe's top prize twice, said. "Last year they should have won the final and have added to their squad this year with Javi Martinez and Mario Mandzukic up front.
"They are going to have a chance. But the dark horse is definitely Dortmund.
"I don't think they are paying too much attention to the league. Their concentration is on the European Cup and their European form has been very good."