The 37-year-old full-back, who now plies his trade for Russian outfit Anzhi Makhachkala, was apparently taunted by Zenit fans prior to his side's 2-0 defeat to the reigning Premier Liga champions on Monday.

A photograph has since emerged of a supporter appearing to wave a banana in the direction of the former Real Madrid star as the two teams entered the field.

Zenit today condemned the alleged incident, and vowed to step up their efforts to stamp out racism by working closely with the country's governing body and the police.

"In connection to the publication of a photograph on which a person in the stands made an unethical gesture toward FC Anzhi captain Roberto Carlos, FC Zenit is conducting an investigation of the given episode together with law enforcement officials," read a statement on club website en.fc-zenit.ru.

"Once again, FC Zenit reminds all football fans that racial intolerance is unacceptable. Football unites all people no matter what their social status, skin colour, or confession.

"We have always made every effort possible to prevent racism, however ethnic intolerance and aggression in the stands can be overcome only through joint efforts by law enforcement officials, the Russian Football Union, and clubs."