Twelve police officers were injured during disorder at Leicester's Europa League match with Legia Warsaw.
Leicestershire Police said seven people were arrested following the match at the King Power Stadium on Thursday evening.
Two officers were taken to hospital, one with a broken wrist and the other with concussion, after police responded to disorder which broke out within the away fans’ section during the second half, the force said.
A number of flares were set off and some fans attempted to breach the segregated line, assaulting officers in the process.
Leicester won the match 3-1, which sent them to the top of their Europa League group.
The Polish side’s fans were held back in the stadium at full-time and no further disorder was reported, police added.
The force said a large number of ejections were also made from the ground and the seven arrested remain in custody.
Assistant Chief Constable Julia Debenham said: "While I am pleased that our officers responded well and managed to contain the away fans within their section and minimise contact between them and the home crowd, it’s extremely disappointing that a number of fans acted the way they did and 12 officers were injured during the incident.
"This type of behaviour is not acceptable and we will be investigating the incident fully in order to bring those offenders to justice."