Borussia Dortmund director of football Michael Zorc has said his team need to beat Ajax in the Champions League next week to give themselves a chance of progressing from a "unique" group.
Dortmund have been drawn with Ajax, Manchester City and Real Madrid in Group D, and the back-to-back Bundesliga winners will be cheered on by a sell-out crowd of almost 66,000 when they face the Dutch side at the Westfalenstadion on Tuesday.
Zorc - a midfield legend for the club and a Champions League winner with them in 1997 - told kicker: "We will do all we can to survive the group.
"We know we have our qualities, but we also know Real Madrid are favourites in this unique constellation, with four current champions and three former Champions League winners.
"It is going to be hard work. We need to leave the door open to advance, and therefore we need to beat Ajax at home next week. It is about the three points."
But he also urged Dortmund not to take their eye off domestic matters - before they begin their Champions League campaign, they play Bayer Leverkusen at home on Saturday.
"We should not talk about Manchester City or Real Madrid now," Zorc said. "Leverkusen and Ajax are two extremely important home matches - two opponents we want to beat by all means."
Domestically, Dortmund beat Bremen at home before being held to a 1-1 draw at Nurnberg and Zorc said: "We currently make too many mistakes when we have the ball. We are not there yet."
He praised the contribution of forwards Mario Gotze and Marco Reus, saying: "Marco has the ability to find the right answer in every situation.
"He is fast when we are counter-attacking and has the technique to win one on ones. But you should not expect him to play at his highest level in 34 league matches, with Champions League and national team [games] added on top."
"Mario has shown he is fit again and in good form. Now it is a question of energy, how long he can show it on the pitch. Every match, every week helps him. He can play all three positions behind our striker, and he can play them equally well."