Jose Mourinho said Gianluca Prestianni will have no future at Benfica if he is found guilty of racially abusing Real Madrid's Vinícius Júnior.
The Argentinian is being investigated by European governing body UEFA following allegations made by Vinícius during last month's Champions League playoff in Lisbon.
Prestianni, who denies the claims, was handed a provisional one-match ban, meaning he missed the second leg of that tie last week -- which Madrid won to advance to the round of 16 -- while UEFA launched its investigation.
The 20-year-old faces more severe punishment if found guilty.
Benfica manager Mourinho was initially criticised for his response, in which he suggested Vinicius had incited the crowd with the way he celebrated his goal. He also did not condemn Prestianni.
However on Sunday, the Portuguese told reporters ahead of Benfica's game on Monday that he was "completely, utterly opposed to any kind of discrimination or prejudice or ignorance or stupidity."
The 63-year-old added at a press conference: "If my player did not respect these principles, which are mine and Benfica's as well, then that player's career with a coach named Jose Mourinho and at a club named Benfica will come to an end.
"I am not a scholar, but I am not ignorant either. The presumption of innocence is a human right, isn't it?
"I stand by my opinion. If the player is indeed guilty, I will never look at him the way I looked at him before, and with me, it's over.
"But I have to put many 'ifs' in front of it."
The flashpoint occurred after Vinicius had scored the only goal of the first leg early in the second half at the Estadio da Luz.
Prestianni covered his mouth with his shirt at the time he was alleged to have aimed a comment in the Brazilian's direction.
Information from PA was used in this report.
