To Borussia's credit, players and coach didn't hide behind the unfortunate nature of the defeat in the league but openly addressed their shortcomings in the wake of that disappointment in Saxony. Tuchel criticised "a lack of precision, too many mistakes under pressure, too few shots on goal" while goalkeeper Roman Bürki attested to "a lack of concentration." New captain Marcel Schmelzer, taking over from Mats Hummels (now at FC Bayern), bemoaned Dortmund giving the ball far too cheaply in the face of Leipzig's pressing.

The story must not repeat itself in the Polish capital, the 28-year-old left-back warned: "Legia haven't been in the Champions League for 21 years. They will run their socks off just as Leipzig did."

Dortmund won't be the only side struggling to play to their potential against Ralph Hasenhüttl's high-intensity side but the concerns about their performance levels have deeper origins. The departure of Hummels, Henrikh Mkhitaryan (to Manchester United) and Ilkay Gündogan (to Manchester City) has ripped out the very heart of the team in the offseason. Tuchel and sporting director Michael Zorc have sought to fill the void by signing eight new players, but the Leipzig game hinted at a more arduous rebuild than was perhaps anticipated.

Seasoned observers such as Süddeutsche Zeitung's Freddie Röckenhaus noted that Dortmund suffered both from lack of structure in their build-up game as well as from a more intangible, harder-to-fix lack of presence on the pitch. Marc Bartra, who replaced Hummels in central defence, has a similar gift for accurate passing from the back but not yet the same authority, especially in the dressing room.

Hummels' boundless self-belief wasn't always easy to stomach for coaches and teammates but it was infectious. Schmelzer is a much more quiet character whose long-term prospects are also uncertain in the wake of the arrival of Euro 2016 breakout star Raphael Guerreiro. Midfielders Gonzalo Castro and new signing Sebastian Rode (from FC Bayern) have leadership potential if not quite the extraordinary skills that will guarantee them regular starting positions.

Julian Weigl, 21, is still young and prone to fluctuations in performance. And the two World Cup winners, André Schürrle and Mario Götze, first need to consolidate their own performances before either can grow into a role model for younger, less experienced recruits such as Ousmane Dembélé or Emre Mor, incredibly gifted attacking players on a steep learning curve in terms of collective movement and defensive duties.

After an impressive preseason and start to their domestic campaign, the focus is threatening to shift from the thrilling possibilities afforded by Dortmund's deepest and most varied squad to the instability that's inherent in any big upheaval. Time, as well as Tuchel's considerable skill in bringing out the best in players, will work in the club's favour but time has to be earned, too. Dortmund need a win in Warsaw to look at the imminent future with more confidence.

It'll be Tuchel's debut in the Champions League, "a little bit like Christmas or my birthday," the 43-year-old said. The former Mainz 05 boss tried to strike a lighter note on the eve of the game, wondering whether his yellow socks would match the suit he's required to wear in Europe's top club competition. Fears over Dortmund's problems were overblown, he insisted: "The game [at Leipzig] wasn't that bad, there is no need throw our hands up in despair and question our ability to compete in Warsaw. There is no need to worry."

Not yet, in any case. And the danger that Legia will pose to Dortmund's equilibrium will also constitute an opportunity, of course: the chance to come together as a team in the sell-out Wojska Polskiego stadium.