Crowd trouble during Burnley's game against Hannover 96 resulted in a police officer and a steward being taken to hospital.
The police officer received treatment at Burnley General Hospital for a head injury while the steward was taken there with a dislocated shoulder.
Two stewards also suffered minor injuries and were treated at the scene.
The match was abandoned at half-time, after the German supporters stormed towards the home section in the Cricket Field Stand, breaking up and throwing seats.
Police are now appealing for fans with any footage of the violence to share it with them.
Chief Supt Chris Bithell said: "Our investigation into the incident is very much ongoing and we are determined to identify those responsible for causing injury and criminal damage at the Turf Moor stadium.
"Although we have received some footage which shows the incident, we would like to hear from anybody else who filmed the disorder, which began shortly before half-time.
“The disorder we saw yesterday has no place in football, and certainly not in Lancashire. Children and families were in attendance at what was a pre-season friendly match, which should have passed peacefully and without incident – but which ended up being abandoned due to the behaviour of some of the travelling Hannover fans. Both the constabulary and Burnley FC condemn this behaviour.
"Overnight we have collated and trawled through footage of the disorder, but we believe there will be more people who have videos on their phones which could help with our ongoing investigation.
"Anybody who has such footage is asked to send it to us as soon as possible.
Chief Supt Bithell said that a proportionate policing operation was in place based on pre-game intelligence, however the behaviour of many Hannover fans before and during the game was confrontational from the outset.
"Forty minutes into the game a large group of Hannover fans attempted en masse to breach segregation and attack home supporters," he said. "This violence escalated with police officers and stewards being attacked, and ultimately we decided in consultation with the referee and the club’s grounds safety officer that the game could not continue.
"During the disorder Hannover fans also caused damage to the stands by ripping out seating, before using it as weapons and missiles against officers and grounds staff.
"Extra resources were quickly drafted in from across the county and the visiting Hannover fans were escorted from the stadium and away from the ground to ensure no further disorder took place.
“We are now continuing to work closely with staff and managers at Burnley FC, and their co-operation has been very much appreciated. Similarly, we would like to thank the fans who co-operated and left the ground without incident once the game had been called off."
Anybody with footage is asked to send it to police using the ‘Report a Crime or Incident’ form on the force website at http://socsi.in/HRg64