Benfica's Gianluca Prestianni has received a provisional one-match suspension after Real Madrid's Vinicius Jr reported alleged racist abuse during last week's Champions League meeting.
It means the Argentine winger is set to miss the second leg of the tie in Madrid on Wednesday (20:00 GMT).
Uefa has imposed the ban on a provisional basis, pending the result of a full investigation by an ethics and disciplinary inspector.
The European governing body said further punishment could be handed out once that investigation is completed.
Vinicius told referee Francois Letexier that he had been racially abused by the Argentina winger during the first leg of their Champions League knockout phase play-off tie in Lisbon last Tuesday.
Prestianni has denied racially abusing the Brazilian, and Benfica said they would appeal against the decision despite the belief it is unlikely to have any "practical effect" before Wednesday's game.
Last week's first leg was halted for 10 minutes after Vinicius alerted on-field official Letexier to the second-half incident, before he and his team-mates temporarily left the pitch.
It came after Vinicius, 25, scored a stunning goal and then received a yellow card for his celebrations in front of the Benfica supporters.
Benfica manager Jose Mourinho, who is suspended for the second leg following his sending off later in the match, was criticised for his post-match comments after saying he believed that Vinicius had celebrated disrespectfully.
Because of his ban, Mourinho will not speak to the media before the match, with assistant coach Joao Tralhao undertaking media duties at the Bernabeu instead.
Uefa's action means that, as it stands, Prestianni will miss the second leg of the Madrid tie, even though the investigation is still to be completed.
European football's governing body said this is because there was enough evidence to support a "prima facie violation" based on the evidence available.
It added: "This is without prejudice to any ruling that the Uefa disciplinary bodies may subsequently make following the conclusion of the ongoing investigation and its respective submission to the Uefa disciplinary bodies."
Responding to the sanction, Benfica said it "regrets being deprived of the player while the process is still under investigation".
The club added it would launch an appeal "even though the deadlines in question are unlikely to have any practical effect on the second leg of the Champions League play-off."
Benfica also reaffirmed its commitment to combating all forms of racism and discrimination, values which it said "are part of its historical identity and are reflected in its daily actions, its global community, the work of the Benfica Foundation, and major figures in the club's history, such as Eusebio".
'Uefa had to move fast' - analysis
Action was demanded of Uefa after the shameful scenes at the Estadio da Luz last week.
And it has shown it is prepared to move quickly.
European football's governing body took just 16 hours to open a disciplinary case against Prestianni.
Three working days later and he has been banned, pending the result of a full investigation.
Uefa's ethics and disciplinary inspector says there is a prima facie case against the Argentina international.
It means that on the initial assessment, the evidence presented is adequate to support the charge of using discriminatory language.
It might seem like a strange step, jumping the gun before a full ruling.
But Uefa has precedent for applying an interim ban in such a case. It shows it recognises when unacceptable behaviour requires fast action.
In 2021, Slavia Prague's Ondrej Kudela was accused of racially abusing Rangers' Glen Kamara in the second leg of a Europa League tie at Ibrox.
Much like Prestianni, the Czech Republic international had covered his mouth before approaching Kamara.
In identical timing to Prestianni, Uefa issued an interim one-game ban two days before Slavia Prague were scheduled to play Arsenal in the next round of the competition.
Eight days later, Kudela was banned for 10 games after Uefa found the case proven.
Uefa had to move faster this time because the next game was just a week away. But it has shown consistency in acting when the evidence demands it.
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