Celtic's Champions League trip to Ajax was marred by a clash between supporters and police in the centre of Amsterdam before kick-off, with 15 fans arrested.
Amsterdam Police said that fans armed with bottles and sticks attacked plain-clothed officers in an incident described as "coming out of nowhere".
Eight police officers were injured with one knocked unconscious following the fighting in Dam Square in the city centre.
Police said the majority of those arrested were Celtic fans, although it is believed that supporters from other clubs were also involved.
"At the end of the afternoon a large group of Celtic supporters attacked police officers in plain clothes," a spokesman said.
"Eight were injured and one was knocked unconscious.
"A few of them had broken noses and needed stitches above their eyebrows and on their lips.
"Bottles and sticks were used in the attack which came out of nowhere.
"There were 15 arrests, mostly Celtic supporters."
Celtic lost the match 1-0 and face an uphill battle to reach the knockout stages of the competition.
Celtic boss Neil Lennon acknowledged that it will now be difficult to reach the last 16.
The Armagh man said: "I thought we were second best in the first half – some players' performances weren't anywhere near their best.
"We've left ourselves a lot to do. The last game, at the Nou Camp, is not the easiest place to go," he added.
"But there's still a lot to play for in the group."
Lasse Schone's goal was enough to avenge the defeat Ajax suffered in Glasgow.
Even if Celtic beat Milan at home in their next game, they will probably need to take something from the Nou Camp showdown to progress.