The 25-year-old has claimed that opposing players from a team in Argentina called him discriminatory names before a game almost 12 years ago.
"It was in the hotel before the match," Campbell said during an appearance for the North East charity Show Racism the Red Card.
"You recognise some of the words that they call black people. They were giving us all that. I couldn't believe it. I was quite young at the time, about 13. It was a bit of a shock. That was the first time I really remember a stand out incident."
Campbell was at the centre of a police investigation last year after he was allegedly racially abused on social network site Twitter.