Police are trying to trace an Arsenal fan who threw a banana at Tottenham's Gareth Bale during Sunday's north London derby at White Hart Lane.
Metropolitan police officers said they had begun an investigation into the incident, which happened in the 27th minute, and Arsenal have pledged to ban the fan for life if he or she is identified.
Bale, who scored the opening goal in Tottenham's 2-1 win, is sometimes a target of chants from opposition fans who claim he "looks like a chimp".
CCTV footage of the away section of the crowd is being examined and Tottenham are helping with the investigation.
A spokesman for the Metropolitan Police said: "Police are investigating after a banana was thrown onto the pitch from the away section of supporters during the Tottenham Hotspur v Arsenal match at White Hart Lane on.
"There have been no arrests, and inquiries continue to try to identify the suspect."
Arsenal have said they operate a zero tolerance policy and will ban anyone found to have thrown the banana.