The Scot believes that their poor domestic campaign means they will be fully concentrated on winning their second European crown.
Die Borussen's last-16 tie with Shakhtar Donetsk is poised at 2-2 following the first leg in Ukraine.
Meanwhile, Ferguson also singled out their domestic rivals Bayern Munich - runners-up twice in the past three years - as potential winners.
"It is a very open tournament," FIFA.com quotes Ferguson as saying.
"Bayern have always had capable and confident teams. 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."
Jurgen Klopp's men finished top of Group D ahead of Real Madrid without losing a game.