In three group matches, Spain fielded three different centre-back pairings: Maria Mendez and Laia Aleixandri against Portugal, Irene Paredes and Laia Aleixandri against Belgium and Maria Mendez and Irene Paredes against Italy.
It was a forced change in the first game, as Paredes was suspended for picking up a red card against the Czech Republic in qualifying, but a rather surprising one afterwards, as Montse Tome still hadn't found her preferred partner.
"Each of them has their strong points," commented Mendez in the mixed zone after the game against Italy.
"I feel comfortable with all of them. We help each other out, no matter who's playing, we're all playing at a very high level. It's a very long tournament, and we all have to be ready to play in case something happens."
Spain have a total of four central defenders, but only two dedicated to the role: Mendez and Paredes. Aleixandri can also play in midfield, while Jana Fernandez, who trained as a central defender, usually plays as a right-back.
Scoring more to compensate
This alternation between pairs makes it more difficult for them to work together when it comes to dealing with set-pieces or counter-attacks.
Justine Vanhaevermaet's header from Tessa Wullaert's corner gave Belgium their first goal against Spain in the group stage, while Ona Batlle and Paredes presented the ball perfectly for Hannah Eurlings' equaliser in the same game.
If the Belgians, who had been soundly beaten 5-0 by France in their warm-up match, were unable to keep up the pace afterwards to hold on for a draw, it was mainly due to the Spanish attack rather than their defence.
"That's something we've improved since the Nations League. Before, our opponents would put a goal past us and we didn't know how to respond. Now we can relax when that happens," says Mendez.
"That's the most important thing in a league like this, to always be able to come back."
Proof that if the Spanish defence doesn't get the job done, they can always make up for it by scoring at least one more goal. Against Belgium, La Roja scored four more goals. Only three against Italy, who had opened the scoring after a ball was poorly given away from a set-piece.
These three goals conceded through the same mistakes against nations considered inferior to reigning world champions Spain are worrying Spanish journalists, who dream of seeing La Roja finally progress beyond the quarter-finals of a European Championship.
"The 'but' of Montse Tome's Spanish team is in defence," writes El Pais, for example.
A taboo subject
Spain's weakness also reassures the Swiss players, who qualified for the final phase of their competition at the last minute thanks to an equalising goal against Finland.
If the home side are dreaming of a shock victory against Spain, Alayah Pilgrim is well aware that she will have her say as a striker.
"They have incredible players, they are all at a high level. But I think they also make mistakes, especially in defence. They're stronger in attack than in defence, they're human beings. I think we'll have our chances too," she explained.
Spanish boss Tome is annoyed that a question on the subject is being asked at a press conference on the eve of the quarter-final clash.
"I'd like to ask you what you mean by defensive weaknesses," she replied to the journalist who put the question to her.
"What I know is that we're the professionals in this area, and we're also the ones who understand the team best."
She continued: "It's obvious that this team wants to improve in every area, but we've only conceded three goals. We have very good defenders, incredible players who have proved their talent, their worth and their ability for a long time.
"I don't think that's a weakness. Attack and defence are collective things. We need the defenders to help us get the ball out in attack and the forwards to press when we lose the ball, as well as the wingers, who have to start defending. It's a team effort."
However, her Swiss counterpart has clearly identified these shortcomings and Pia Sundhage explained at the press conference how the speed of Iman Beney and Nadine Riesen on the flanks, or Sydney Schertenleib in the centre, could be useful on the counter-attack.
"If the penultimate pass is accurate, we can create chances," she promises.
Captain Lia Walti is more cautious: "If they always have the ball, it's because they defend extremely well. They get the ball back very quickly and that's what's going to test us."
So, is Spain's defence a real weakness or just a red herring? The question will be answered on Friday evening at 21:00 CET.