Celtic could face disciplinary action from UEFA after their fans let off a flare during Thursday’s match against Dinamo Zagreb.
Croatian police then intervened — appearing to spray the away supporters with a liquid — near the start of the Europa League encounter.
Unconfirmed reports suggest local police used tear gas in order to control fans of the Scottish Premiership outfit.
A bright red flare lit up the away end during the opening stages of the Europa League encounter before the police moved in to try to stop any potential trouble from erupting during the game.