Real Madrid could face disciplinary action from Uefa for the banners unveiled before their 3-1 win against bitter rivals Atletico last week.
The La Liga leaders unveiled massive pieces of artwork celebrating their 11 Champions League wins.
And Atletico – who went on to lose the first leg 3-0 – were the target of a cheeky dig on them.
The banners asked “tell me how it feels” to Atletico fans to lose the games while Real sit with the most Champions League wins in Europe.
But Spanish publication Sport, the situation is similar to a few previous cases where teams have been sanctioned over banners.
Uefa fined Ajax for their sign against “modern football” when they played Manchester City last October.
Bayern Munich had part of their stadium closed for their match against Manchester United after a homophobic banner was held up against Arsenal’s Mesut Ozil in a previous game.
Bayer Leverkusen were given a £15,000 fine for their offensive banner when playing Atletico Madrid,
Barcelona and Rapid Vienna have also been sanctioned over their use of banners.
Cristiano Ronaldo netted a hat-trick to help Real put one foot into the Champions League final.