Chelsea have vowed to ban any supporter found responsible for coin-throwing during Sunday's FA Cup fifth-round match against Manchester City at Stamford Bridge.
It appeared objects were thrown from the lower section of the Matthew Harding Stand as City celebrated David Faupala's equaliser after 37 minutes of the contest.
Referee Andre Marriner was later seen collecting three objects from the corner of the pitch. The first appeared to be a coin.
A Chelsea spokesman at half-time condemned the action and said if evidence can be found of who is responsible they would be banned from the stadium.
"We condemn such idiotic and dangerous behaviour and if we can identify those responsible then we will ban them from Stamford Bridge," the spokesman said.
"It's worth noting it's a criminal offence too and we will support any police prosecution, if we can identify, along with the police, those individuals responsible for that behaviour today."
Chelsea interim boss Guus Hiddink said: "I condemn it strongly. Those people, those persons, they must not come into stadiums."
City boss Manuel Pellegrini was unaware of the incident until he was informed after the match.
It was the second incident of coin-throwing in the FA Cup this weekend.
West Brom's Chris Brunt was struck by a coin thrown from the visiting supporters' section in his side's loss at Championship Reading on Saturday.