Uefa opened an investigation into four Real Madrid stars including Kylian Mbappe and Vinicius Junior on Thursday for alleged "indecent conduct" during their Champions League last 16 win over Atletico Madrid.
Madrid's two superstar forwards, as well as defender Antonio Rudiger and midfielder Dani Ceballos, face potential punishment ahead of their quarterfinal first leg clash at Arsenal on April 8.
"A Uefa Ethics and Disciplinary Inspector has been appointed to investigate allegations of indecent conduct by Real Madrid CF players," said the European football governing body in a statement.
Spanish media reports suggested Real Madrid players are being scrutinised by Uefa for the manner of their celebrations after the win.
Uefa and Real Madrid did not immediately respond to an AFP request for comment.
Record 15-time champions and current holders Madrid beat their rivals on penalties at Atletico's Metropolitano stadium on March 12 after a 2-2 aggregate draw.
The night ended in controversy after Atletico forward Julian Alvarez had a penalty controversially disallowed in the shoot-out for supposedly touching the ball twice.