Uefa says there were “isolated incidents of racist chanting” while the Dutch team were taking part in a pre-tournament training session in Krakow.
The Dutch squad were greeted loud jeers, abuse and monkey chants during the training session and moved to the other side of the pitch.
Captain Mark van Bommel, who visited a former Nazi death camp with his teammates on Thursday, called the chanting disgraceful.
“It is a real disgrace, especially after getting back from Auschwitz, that you are confronted with this,” he said.
“At least now we know what we can encounter,” Netherlands coach Bert Van Marwijk was reported as saying. “We will take it up with Uefa and if it happens at a match, we will talk to the referee and ask him to take us off the field.”
Uefa said initially it had no plans to order an investigation, but confirmed on Friday that racist abuse had taken place. It said in a statement: “Uefa has now been made aware that there were some isolated incidents of racist chanting that occurred at the open training session of the Dutch team.”
Despite the complaints, the Dutch Football Association told Uefa, European football’s governing body, that it did not believe the abuse was racially motivated, while before issuing its statement, Uefa said it was satisfied that the chants were a protest because Krakow had not been made one of the host cities for Euro 2012.
The Dutch team were travelling to Kharkiv, Ukraine on Friday. The Netherlands, World Cup runners-up, open their Euro 2012 Group B campaign against Denmark in Kharkiv on Saturday.
The problems reportedly occurred when players started their training session on Wednesday with laps of the pitch and were apparently greeted by monkey noises and jeers. The session, at Wisla Krakow’s stadium, was crowded with more than 30,000 Poles although Krakow is not staging any matches.
Uefa president Michel Platini said it should be up to the referee to handle racism complaints after some players indicated they would walk off the pitch if it occurred in matches.
“Our understanding is that it was an isolated event and from a small minority. It is a reminder, however, of the issues which could potentially arise,” said Danny Lynch, of the UK-based “Kick It Out campaign”.
“Our colleagues, fellow campaigners and those from governing bodies on the ground at the tournament are keeping a close watching brief and we hope any incidents are dealt with swiftly and effectively,” Mr Lynch told Channel 4 News.
The families of two of England’s black players, Alex Oxlade-Chamberlain and Theo Walcott, decided not to attend the tournament because of potential problems.
Mr Platini has said referees would halt or even abandon matches if there was serious racism from the stands during Euro 2012. But he warned that any player who walks off the pitch in protest – which Italy’s Mario Balotelli has threatened to do – will be yellow-carded.
The Polish and Ukrainian governments have worked hard to try to dispel any fears of racism but a BBC Panorama documentary suggested it was prevalent among some fan groups.