Atletico Madrid have grown accustomed to slaying Europe's giants in the Champions League under Diego Simeone, but ending Leicester City's run Wednesday may prove even tougher than ousting Barcelona or Bayern, according to Filipe Luis.
"We're not favourites. We don't believe that," said the Brazilian left-back on Monday despite the vast gulf in Champions League experience between the sides.
Atletico are in their fourth straight quarter-final and missed out by the narrowest of margins in two final defeats to cross-city rivals Real Madrid in the past three years.
However, the Spanish side are all too aware of what Leicester are capable of after the Foxes dumped out their La Liga rivals Sevilla en route to the last eight in their first ever appearance in the competition.
"Maybe for us we can play better against these teams, Barcelona and Real Madrid, because they have the ball and they control the game, but when we have to initiate the style of play it's not going to be easy," added Filipe Luis, who kept Gareth Bale quiet as Atletico held Real to a 1-1 draw on Saturday.
"It's also going to be difficult for them because we know how to play these quarter finals. We have played three in the last three years, so we are prepared."
Filipe Luis said last season that Atletico had used Leicester's remarkable run to Premier League glory as inspiration as they saw off Barca and Bayern over two legs before falling just short against Real on penalties in Milan.
Whilst not on the scale of Leicester's title triumph, Atletico also upset the odds by breaking Barca and Madrid's hegemony when they won La Liga three seasons ago despite a huge financial disadvantage.
"The difference between teams' budgets is something to remember, but in the end it doesn't have to be definitive," Atletico president Enrique Cerezo said last week.
"It was the same for Leicester, they were competing with teams like Chelsea, Manchester City, Manchester United so them winning the Premier League was a huge achievement."
More impressively, though, unlike Leicester, Atletico have been able to build a sustained period of success under Simeone.
Leicester's last visit to Spain back in February, when they lost 2-1 to Sevilla in the first leg of their last-16 tie, was the last straw for the club's Thai owners as title-winning manager Claudio Ranieri was sacked with the English champions plunging towards the Premier League relegation zone.
One of Ranieri's former assistants, Craig Shakespeare, was put in charge on a temporary basis until the end of the season and has overseen a dramatic turnaround in Leicester's fortunes.
Until Sunday's 4-2 defeat at Everton, Shakespeare had won all six games since taking over, including a 2-0 second-leg win over Sevilla, to move eight points clear of the drop zone.
"It's about confidence," said Leicester goalkeeper Kasper Schmeichel, who saved a penalty in each leg against Sevilla.
"Just as you can go on a losing run, you can go on a winning run as well. We've got the players to do that. We've always been capable of doing that."
Simeone, though, insists his analysis of Leicester hasn't been changed by their sudden upturn in form.
"For many people we are now facing a different team to the one we got in the draw," said the Argentine.
"But we always knew it was going to be a difficult, hard-fought game against a team that in many aspects is similar to ourselves."