Newcastle striker Demba Ba has criticised spectators who allegedly racially abused players during Saturday's 0-0 friendly draw at Den Haag.
Reports claim some sections of the home crowd at the Kyocera Stadium aimed chants at several members of the Magpies' team, prompting the club to raise the issue privately with their hosts.
Many of the Newcastle players did not hear the abuse, although midfielder Cheick Tiote, who played his football in Holland with FC Twente before moving to Tyneside was said to be furious after the game.
Senegal international Ba told the Evening Chronicle: "I did not hear it because I was focusing on the game.
"If they do that, they are really stupid dudes. They have to grow up.
"People have to man up. There are many people on earth and you have to be responsible."