Wolverhampton Wanderers told fans they faced prosecution after objects were thrown at Manchester City players during the teams' Premier League match.
After City celebrated Raheem Sterling's opening goal, an announcement told supporters "numerous instances of objects being thrown" had been seen.
One of the items was a metal hip flask.
BBC Radio 5 Live's football correspondent John Murray, at Molineux for Friday's game, said it "could have caused serious damage".
Referee Martin Atkinson gave the object - thrown from the Jack Hayward Stand containing Wolves supporters behind keeper Rui Patricio's goal - to fourth official Andre Marriner, who informed security.
Fans were told over the public address system that CCTV would be used to identify those responsible, and that they could face criminal charges and a stadium ban.
Speaking after the game, Wolves manager Nuno Espirito Santo said: "It is no good. Let's not do it. That is not us."
The incident happened after City had taken a 1-0 lead in an action-packed first half before Wolves went on to win 3-2 in the last minute.
Manchester City keeper Ederson was sent off on 12 minutes and Sterling then had a penalty saved twice after the video assistant referee ordered a retake for encroachment from Wolves captain Conor Coady. But the City forward scored from the rebound on the second spot-kick.
Sterling scored a second after half-time, but Wolves levelled through Adama Traore and Raul Jimenez before Matt Doherty won it with a shot from the edge of the area late on.
The result leaves City in third place in the Premier League, 14 points behind leaders Liverpool, who have a game in hand. Wolves moved up to fifth place, just two points behind Chelsea in fourth.