Before a ball was even kicked, the issue of racism flared up at the European Championship after Netherlands players said Polish spectators made monkey chants at them during a training session.
The Dutch federation didn't file a complaint to UEFA but European football's governing body said on Friday it had been informed there were ''isolated incidents of racist chanting'' and that it will take action if there is a repeat of such abuse.
''We heard it because we were jogging right by the stands,'' team captain Mark van Bommel said of the incident. He said he was happy training switched to the other side of the Krakow training ground in southern Poland.
The chanting was not widespread since coach Bert van Marwijk said he failed to hear anything untoward, only lots of noise which made him switch to the other side.
Even though the information only leaked out a day late - and was initially denied by Dutch officials - it was back on the agenda at the team's news conference ahead of the opening Group B game between the Netherlands and Denmark on Saturday.
Van Marwijk sought to play down the controversy, saying: ''I'm trying to be as nice possible.''
There was comment too from retired Netherlands great Ruud Gullit, who is black.
''It is sad that we have to talk about this - we don't need this,'' Gullit said Friday at the Polish foreign ministry, where he was helping to launch a UEFA-backed campaign to combat discrimination at the eight Euro 2012 stadiums.
The ongoing threat of racism has been a key issue since the tournament was awarded to co-hosts Poland and Ukraine in 2007.
There was a party atmosphere in Warsaw ahead of the opening match, between Poland and Greece. But while UEFA attempted to play down the controversy on Friday, the debate has persisted despite claims by Polish and Ukrainian governments that racism was being confronted.
''The two countries have worked very hard to organize this tournament and we should not disturb this because 10 people are chanting in a stadium,'' said UEFA media director Alexandre Fourtoy.
Van Bommel said the chants came from one end of the stadium in Krakow as the Dutch squad trained Wednesday in front of about 25,000 spectators before leaving to face Denmark at Kharkiv, Ukraine. Such was the disgust among players that they moved to the other side of the pitch.
''We will not accept that one of us is confronted with monkey chants,'' Van Bommel told Friday's edition of De Telegraaf. ''We will point it out to the referee and if such chants are heard again we will ask him to intervene.''
Ibrahim Afellay, a winger of Moroccan descent, was also quoted Friday as saying that members of the Dutch squad were taunted.
The incidents 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.
The southern city was overlooked by Poland's football federation as one of its four cities hosting matches at the Euros.
''I don't think that if you are frustrated about not having the tournament in your city, you do it (complain) in this way,'' said Gullit, who captained the Netherlands to the 1988 title.
Insisting there was still no evidence to prove that the racist abuse actually occurred, Fourtoy said UEFA will consider stewarding open training sessions.
''We are more worried that this incident could be given disproportionate importance,'' he said. ''I think it's unfair for Poland and Ukraine to be considered racist countries - South Africa in the 1980s was a racist country.''
A recent British television documentary, entitled ''Stadiums of Hate,'' fueled concerns about fans' behavior 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 broke football's rules and acted alone by walking off the field.
''UEFA has a zero tolerance policy when it comes to discriminatory behavior and has given the power to referees to stop matches in case of any repeated racist behavior,'' UEFA said Friday.
UEFA's top administrator, Gianni Infantino, later suggested that its independent judicial bodies had scope to rescind yellow cards in some cases.
The sole black player on the Czech Republic's team, Theodor Gebre Selassie, said he hoped racism wouldn't happen.
''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.''
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AP Sports Writer Raf Casert in Krakow and Associated Press writer Karel Janicek in Wroclaw contributed to this report.
