Bayern Munich have been almost untouchable in the Bundesliga but their edgy performance against Arsenal suggested that the lack of competition at domestic level could hinder their European ambitions.
Bayern again found the Champions League a different proposition as they struggled to break down a surprisingly cautious Arsenal in the first half of Tuesday's game and showed vulnerabilities in defence when the visitors came at them in the final half hour.
The last time Bayern failed to win a competitive game was also in the Champions League last December, when they squandered a 2-0 lead and lost 3-2 at home to Manchester City.
Arsenal manager Arsene Wenger also faced Bayern last season in the round of 16 and was able to make a brief comparison between last year's Champions League-winning side, coached by Jupp Heynckes, and Pep Guardiola's version this year.
"I thought Bayern were very vulnerable defensively, we didn't take advantage of that," he said. "I felt the situations were there where we could have made more of it."
Bayern, leading 2-0 from the first leg, went ahead with a Bastian Schweinsteiger goal but Lukas Podolski stunned the Allianz Arena when he levelled two minutes later.
But Guardiola's team immediately lost their swagger and Arsenal threatened a second.
"Bayern have weaknesses, like every other team," Arsenal's Alex Oxlade-Chamberlain said.
Any perceived weaknesses in Bayern, however, have not been apparent in the Bundesliga.
Last season's treble winners have won 22 and drawn two of 24 league games this season and scored 72 goals. Their last defeat in the league was against Bayer Leverkusen in October 2012.
When Guardiola recently described the Champions League as a gourmet meal and the Bundesliga as pizza, many commentators took it as criticism of the domestic championship, although the Spaniard denied it was meant that way.
Former Bayern captain Franz Beckenbauer was less than impressed with their display last night, however.
"In the end, it'll be like Barcelona, unwatchable," he said, referring to Guardiola's previous team and their tiki-taka passing game.