"UEFA has now been made aware that there were some isolated incidents of racist chanting," UEFA said in a statement.
Netherlands captain Mark van Bommel has been quoted as complaining about racist chants at one end of the stadium during a training session that was open to the public on Wednesday. About 25,000 spectators attended the session.
"He has heard noises and by moving to the other side, we nipped it in the bud," the Dutch federation said Friday.
Netherlands teammate Ibrahim Afellay told De Telegraaf newspaper that the jeers had "saddened him." However, the Dutch federation said Thursday it did not file a complaint to UEFA.
The Dutch were training in Krakow before leaving to face Denmark in their Group B opener on Saturday at Kharkiv, Ukraine.
The training session came only hours after the team, which for decades has been a reflection of the multicultural makeup of the nation, had made solemn and emotional visits to the former Auschwitz-Birkenau death camps close to Krakow.
Racism has emerged as a key issue for the Euro 2012 tournament in Poland and Ukraine.
A recent British television documentary, entitled "Stadiums of Hate," fueled concerns about fans' behaviour at club matches. The program was shown in Poland earlier this week and the issue dominated questions at the first news conference of UEFA President Michel Platini at the tournament.
Platini promised that referees will stop matches if players suffer racist abuse. But he also warned players they would be shown a yellow card if they acted alone by walking off the field.
"UEFA has a zero tolerance policy when it comes to discriminatory behaviour and has given the power to referees to stop matches in case of any repeated racist behaviour," UEFA said Friday.
The sole black player on the Czech Republic's team, Theodor Gebre Selassie, said he hoped racism wouldn't flare up in the stadiums.
"We don't know yet what the situation will be like at the stadiums," he said, adding that he would not walk off the field. "I'm not ready to give up. I definitely won't leave. I'll stay until they throw stones at me."
AP Sports Writer Raf Casert in Krakow and Associated Press writer Karel Janicek in Wroclaw contributed to this report.Suggest a correction