Madrid prosecutors said that the cases had been quickly dealt with as a result of the fans involved admitting the charges in exchange for a more lenient sentence.
The Leicester fans were in the Spanish capital for Wednesday's quarter-final first leg which the home side won 1-0.
Social media videos had shown a blue smoke bomb was let off while objects were also thrown at police in the Plaza Mayor, a popular tourist stopping off point, where supporters of the English champions had congregated.
Spanish police said eight Leicester fans were arrested for "causing a mess" on Tuesday night.
"We are working with Uefa and the local authorities to establish the full facts of what took place and the reasons for the police response," a Leicester spokesman said on Thursday.
"We will also be liaising with travelling supporters before deciding on any course of action."
Fans claimed police used tear gas and rubber bullets against them as tensions boiled over in Spain and accused the authorities of being overzealous.
Leicester's official fan allocation was around 2,800, but it is believed there were several thousand who travelled to Madrid without tickets.
Some Leicester supporters managed to buy tickets in the home ends of the Vicente Calderon, while Atletico also had a neutral zone at the stadium.
Three police officers and two English fans were injured in clashes.
The eight who were charged appeared in a Madrid court after spending close to 40 hours in detention.