There are reports of serious crowd trouble throughout the day ahead of Milan-Ajax with six people stabbed.
The Champions League match kicks off at San Siro at 19.45 GMT, but the problems started long before fans approached the stadium.
Ajax supporters wreaked havoc in the city centre with 100 of them stopped by police for throwing objects and attacking passers-by.
They ambushed a peaceful protest of farmers in Piazzale Loreto, which had blocked the roads in that area for several days.
Around 20 Ajax fans got out of their bus and attacked the peaceful protestors.
In another incident, a group of Ajax hooligans tried to break into the Milan Point shop in Piazza Fedele, smashing windows and throwing bottles.
It is reported the attack outside San Siro, in which six people between Italians and Ajax supporters were stabbed, was organised as ‘revenge’ for the brawl in the city centre.
Of the six people stabbed, three are thought to be in a serious condition, while three did not need hospital treatment.
Think you know your Italian football? Share your knowledge, tips and comments to win cash prizes in OLBG's tipster competition - £5,000 monthly.