Lucien Favre did not see Jadon Sancho unveil a shirt displaying 'Justice for George Floyd' after scoring during Borussia Dortmund's 6-1 victory over Paderborn.
England international Sancho showed the garment bearing the name of the man who died in police custody in the United States, prompting protests across the country and beyond.
The 20-year-old was shown a yellow card for removing his playing shirt while celebrating the first of his three goals in the Bundesliga game on Sunday.
Dortmund team-mate Achraf Hakimi also displayed a shirt with the same slogan, as the visitors ran out comfortable winners against the team sitting bottom of the table.
"I didn't see it," coach Favre said of Sancho's celebration. "After the game, I heard about him celebrating a goal like that. There was something on a t-shirt.
"What can I say? I don't know why he did that. I didn't see it. I can't judge it."
Dortmund were held scoreless in the first half before Thorgan Hazard broke the deadlock in the 54th minute, setting them on their way to a landslide triumph.
It was a much-needed three points following a midweek loss to Bayern Munich, a result that left them highly unlikely to catch the reigning champions in the title race.
Favre revealed he was not worried by side's failure to score before the break in the absence of Erling Haaland, who missed the game due to a knee injury.
''I only said one sentence during the half-time break: 'We need to keep doing what we're doing'," he said.
"We pressed well, we tired out our opponents, and it was clear that they wouldn't be able to keep up the tempo all the way to the final whistle.
"We wanted to make sure they couldn't hit us on the counter, as they have a lot of pace up top.
"We were able to maintain the intensity we showed in the first half and the only real change we made was some alterations to our wide players' movements."