As Bayern Munich's ninth goal flew past a shell-shocked René Adler in the Hamburg goal on Saturday, it became obvious why their centre-back, Dante, recently revealed that he is finding training sessions harder than some Bundesliga matches. To put it mildly, Bayern have had no equals in Germany this season, racing away with the league at a pace that would shame Usain Bolt, and attention has turned to trying to win the European Cup for the first time since their victory over Valencia in the final in 2001.

Bayern have reached two finals since then, losing to Internazionale in 2010 and Chelsea on their own ground last year, and must overcome Juventus if they are to keep their dream alive.

Juve, who are at home in Wednesday week's second leg, are in their first quarter-final since 2006 and although Bayern are 20 points clear at the top of the Bundesliga, the Italian champions might just provide Dante with the test he has been craving. Whether that is a positive thing remains to be seen, because while the Brazilian's honesty was refreshing, it was also the kind of remark that will provide ammunition for Bayern's enemies when something finally does go wrong for them.

It almost did in the previous round against Arsenal. When Thomas Müller put Bayern into a seemingly unassailable 2-0 lead after 21 of the most one-sided minutes you could wish to see in a first-leg match, the tie looked like a formality. Bayern took a 3-1 lead back to Germany for the second leg and Arsenal's obituaries had already been written before a match that was supposed to be a chastening experience for Arsène Wenger's side. Yet by the end, with Arsenal leading 2-0 and pressing for a winner, it had turned into an ordeal for Bayern and the memories of Chelsea's improbable victory in last season's final came flooding back. So, too, did the defeat to Inter two years ago. Despite winning 1-0 at San Siro, Bayern lost the second leg 3-2 at home and went out on away goals.

This time Bayern escaped but suddenly, for the first time, there were doubts surrounding a side that had previously seemed unbeatable. Perhaps it was too easy for them. In the first leg against Arsenal their swagger earned them rave reviews, yet it does not take a lot for momentum to shift and their lethargy in the second leg was alarming. Bayern were overly complacent, unsure how to defend a lead that meant the visitors had to win 3-0 to go through, while the absence of Bastian Schweinsteiger and Franck Ribéry robbed them of their usual fluency.

Bayern's president, Uli Hoeness, had his own theory about the defeat. "We've been playing like shit for three weeks," he said, although since losing to Arsenal, Bayern have won twice in the league. On Saturday Claudio Pizarro scored four as they beat Hamburg 9-2. And yet the sporting director, Matthias Sammer, still wasn't happy, grumbling about the concession of two goals from corners.

As harsh as it was, he had a point. Bayern might have only conceded 13 goals in the league, but two of Arsenal's three over the course of the tie came from corners. Didier Drogba's equaliser for Chelsea last May was a header from a corner. It is a weakness that can be exploited.

Still it might be clutching at straws to talk about Bayern's weaknesses when they have been in such awesome form. The array of talent at their disposal is so extensive that Arjen Robben often has to settle for a place on the bench, and if they win at Eintracht Frankfurt on Saturday they will have sealed a 23rd league title with six games to spare. They are bidding to reach their third Champions League final in four years, and have beaten Manchester United and Real Madrid in recent seasons. Pep Guardiola will inherit a major force when he arrives next season.

Bayern are slight favourites, but no one is writing off Juventus. After all, the Italian champions are unbeaten in Europe this season and are nine points clear at the top of Serie A after their 2-1 victory at Inter on Saturday. While it is arguable that they do not have quite as much class as Bayern, Antonio Conte has built a resolute, efficient side who will be ready to pounce on the slightest mistake.

Gianluigi Buffon is still one of the best goalkeepers in the world, the back three is imposing, Andrea Pirlo remains as graceful as ever, and the young Frenchman, Paul Pogba, has been a revelation since his arrival last summer. There are question marks against their forwards though.

Yet Juventus will not be overawed about going to the Allianz Arena. They have already won at Celtic and Shakhtar Donetsk this season, and recovered from 2-0 down to draw 2-2 at Chelsea in their opening group match thanks to goals from Arturo Vidal and Fabio Quagliarella.

"I was brought on and scored so I will never forget my Champions League debut," Quagliarella said. "I think it was crucial, because we realised we could take on any team. Chelsea had lifted the trophy three months before, and we had to play our first match there. Even though we were 2-0 down we showed great character and didn't give up – we believed until the end and were rewarded for that."

Bayern have been warned.