Russian football chiefs on Tuesday launched an investigation into an apparent racially-motivated attack on Anzhi Makhachkala's Congolese defender Christopher Samba.
Media reports said that Samba was on his way to the dressing room after the final whistle of Sunday's game at Lokomotiv Moscow, which his side lost 1-0, when a banana came flying from the VIP box, landing nearby.
The 27-year-old player picked it up and threw it back and said afterwards that he hoped it served as an example of "how not to behave".
Russian Premiership security chief Alexander Meitin said the probe would involve scouring security camera and video footage of the crowd to find the culprit.
"Our aim is to find the man who threw banana at Samba," he said. Anzhi also issued a statement, expressing their hope that the fan would be found.
Brazil veteran Roberto Carlos was twice the victim of banana attacks when he played for Anzhi at Saint Petersburg and Samara last year, prompting league bosses to appeal to fans to stop tarnishing the reputation of Russian football.
Premier League spokesman Sergei Alekseyev said the league was ready to do everything to "change the situation" but that legal action was not always possible.
"The stadium in itself is a democratic environment," he said. "The police can seize flares but how can they seize fruit?"