After a superb start to the season Barcelona were brought crashing back down to earth by Real Madrid and Paris Saint-Germain last week, raising fresh doubts about the Spanish champions' ability to compete against the strongest opponents.
Hansi Flick's side have dominated in Spain over the last two seasons, winning back-to-back LaLiga titles, but notably in Europe have fallen short on high-pressure nights.
The Catalan giants have played sumptuous attacking football this season and won their first 11 games across all competitions, but once the quality of their opponents rose, it was a different story.
Barca were beaten 4-2 in Paris by European champions PSG on Tuesday, showing they are still some way from matching Luis Enrique's side.
That was compounded by Sunday's painful 2-1 home defeat by Jose Mourinho's Real Madrid in LaLiga, in which Barcelona's defensive frailties were laid bare again.
A draw would have been an acceptable result and maintained their six-point lead on Madrid in the top flight, but they left far too much space for Los Blancos to exploit in the final stages.
With three minutes to go Eduardo Camavinga raced through on goal and squared for Kylian Mbappe to net his 100th Madrid goal and second of the night to snatch victory.
"In the end sometimes in the big, big games, small things are important and they decide the game and which way they end, and today that was not on our side," Flick told reporters, pledging to improve.
"We know what we have to make better. We speak about this in every training. We will do it, I'm not worried about that.
"It's a part of this game to lose also. In this week, we had two (losses) and it's too much."
However it is a discourse which the German coach has repeated during his tenure.
"We are a young side and we have to mature," said Flick, after Inter Milan ousted Barcelona in the Champions League semifinals in May 2025.
"We are working on it and we have to improve in defence and in other aspects."
LACK OF 'FRESHNESS'
Despite spending good money on Anthony Gordon, Rodri and others this summer, and trying to bring in Atletico Madrid striker Julian Alvarez, Barcelona did not sign a centre-back.
Instead Flick has persisted with Gerard Martin, a converted left-back, playing alongside Pau Cubarsi.
Martin has done well, considering his technical limitations and change of position, but against the world's best strikers is clearly out of his depth.
The defender's poor clearance handed Madrid their first goal against Barca, with Mbappe gleefully capitalising.
To Martin's credit, he did defend well to stop Jude Bellingham and Mbappe in a two-on-one situation early in the second half, which exposed a more structural problem Barca have.
Their high-line defence is easy to breach when the team's pressing is not executed perfectly, with high energy.
Flick suggested Barcelona lacked "freshness" against Madrid, after a gruelling schedule, although his team had an extra day to recover midweek and the coach waited until the final minutes to introduce Gabriel Jesus and Karim Adeyemi.
Barca do have injury problems at the back, with Eric Garcia, Jules Kounde and Andreas Christensen all missing the Clasico, along with midfielder Dani Olmo.
"This may be the most important point, the injuries we have," explained Flick.
Barcelona still hold a three-point lead on Madrid, third, in the title race. They are more than capable of going on another run of victories, but the weeks ahead will pose further interesting tests.
Aston Villa visit Camp Nou in the Champions League on November 3, before Barcelona head to Atletico Madrid on 8 November. A month after that, Manchester City come to the Camp Nou.
Flick has been promising improvement in these type of matches for over two years – perhaps now he will finally focus on implementing it.