FIFA anti-racism adviser Tokyo Sexwale believes black players could boycott the 2018 World Cup and urged Russian President Vladimir Putin to demand tougher action against racism in football.

Sexwale, who was an anti-apartheid campaigner and former political prisoner on Robben Island, is against a boycott but expressed concern about the growing number of racist incidents in the Russian league.

"There is a threat black players will say they are not going to Russia (for the World Cup) - we can't have that,'' Sexwale said on the sidelines of the Doha Goals conference.

"I am talking as a FIFA person and a citizen of the world. It can't go that far. ... Once these things start and you don't act as leaders, these things snowball.''

Russian club FC Rostov coach was forced to apologise for his remarks about "dark-skinned'' players after some in his team threatened to strike.

Rostov coach Igor Gamula said on Friday the club had "enough dark-skinned players, we've got six of the things'' when asked about rumors Rostov could sign a defender from Cameroon.

Sexwale said an apology alone wasn't enough, pointing to how the NBA forced Donald Sterling to sell the Los Angeles Clippers and banned him for life over racism.

"For the Russian federation to be seen to be serious we need them to take stern action. The world took stern action against South Africa (over apartheid), it was expelled from FIFA.

Earlier, UEFA's disciplinary panel found the Russian champion CSKA Moscow guilty for their fans' "racist behaviour" during Manchester City's 2-1 win in Moscow in September.

City captain Yaya Toure directed referee Ovidiu Hategan toward fans making monkey noises at the English club's black players.

Source: Al Jazeera and agencies