Toure thinks that a victory over the Bundesliga winners can provide a platform for progression from a daunting group, which is completed by Real Madrid and Ajax.
He told reporters at the pre-match press conference: "Is it a must-win game? Yes, it's a massive one for us.
"It can be massive for us to get to the second round, we have to get through but we know we have to get a good result.
"The Champions League is the tough competition in Europe we have try to do our jobs and win. We understand the position we are in because we lost in Madrid."
Roberto Mancini's side are under pressure to beat Dortmund after a dramatic late defeat to Real Madrid in their opening match in this year's competition.