UEFA is investigating Vinicius Junior's allegation that he was racially abused by Benfica's Gianluca Prestianni.
It comes amid a backlash against Jose Mourinho and a response from the Portuguese club claiming a "defamation campaign" against their player.
- in line with UEFA regulations - on Tuesday.
The Real Madrid winger scored the goal in his side's 1-0 win, after which he celebrated in front of the Benfica fans before he was allegedly abused by Prestianni.
Prestianni pulled his shirt over his mouth while confronting Vinicius but denies the allegation of racism.
A UEFA ethics and disciplinary inspector has since been appointed to "investigate allegations of discriminatory behaviour".
UEFA regulations state: "Any player or team official found guilty of racist conduct must be suspended for at least 10 matches."
Vinicius' Real Madrid team-mate, Kylian Mbappe, said after the game that he and other Benfica players heard what Prestianni said to Vinicius.
But Benfica released a statement on Wednesday offering their "full support" to their player and suggested a "defamation campaign" is in action against him.
UEFA's investigation is expected to take weeks rather than days, meaning that Prestianni, as it stands, is likely to be available for selection for the second leg of the Champions League knockout round play-off in Madrid on February 25.
Mourinho has been widely criticised for his reaction to the incident after saying of Vinicius: "When you score a goal like that, you celebrate in a respectful way."
Later asked if he believed Vinicius "incited" the home crowd and players with his celebration, the Benfica boss added: "Yeah, I believe so. The words they exchange, Prestianni with Vinicius, I want to be independent. I don't comment about it.
"When he was arguing about racism I told him the biggest person in the history of this club was black [Eusebio]. This club, the last thing it is is racist, so if in his mind it was something in relation to that, this is Benfica.
"There is something wrong because it happens in every stadium. Every stadium that Vinicius plays [in] something happens. Always."
Your Site' Jamie Carragher, speaking on CBS, described Mourinho as "a guy who celebrates and antagonises the opposition probably more than any coach has ever done."
"Anyone can celebrate how they like," Carragher added. "You shouldn't get racially abused no matter what.
"It feels a little rich coming from Mourinho.
"Remember him running down the touchline at Old Trafford? I remember in a cup final against Liverpool when Chelsea scored very late, [Mourinho was] telling all the Liverpool supporters to shut up.
"It's a bit rich coming from him to be having a pop at Vinicius Jr for his celebration. It's a huge goal in a big Champions League game, he's more than entitled to celebrate how he likes."
Meanwhile, Micah Richards described Mourinho's comments as "hypocrisy".
"Mourinho is someone who I absolutely love as a coach," the Your Site pundit said on CBS' Champions League coverage.
"I expect better from him because he's a powerful person within the sport. A lot of people listen to what he says.
"It's hypocrisy from him talking about Vinicius Jr when he celebrates how he wants."
Former Real Madrid midfielder Clarence Seedorf, who was working as a pundit at the game, said Mourinho made "a big mistake" with his comments.
He said on Amazon Prime: "I think he made a big mistake today to justify racial abuse. I'm not saying that was the case today but he mentioned something more than today.
"He said wherever he goes these things happen so he's saying it's OK when Vinicius provokes you, that is it OK to be racist and I think that is very wrong.
"We should never, ever justify racial abuse."
Meanwhile, anti-discrimination charity Kick It Out has accused Mourinho of gaslighting for his response to Vinicius Jr's allegations of racist abuse.
A Kick It Out statement said: "When anyone reports discrimination in football, or anywhere, the first priority is that they are listened to and feel supported.
"Focusing on Vinicius Jr's goal celebration or the history of the club, instead of acknowledging the report, is a form of gaslighting.
"This approach not only harms the individual affected but also sends the wrong message to others around the world who may have experienced similar situations.
"Leaders in football have a crucial role in setting standards, and moments like these call for responsible leadership that reinforces respect, inclusion, and accountability.
"We look forward to a thorough investigation into this incident, with appropriate accountability linked to the outcome."
