Two Chelsea fans were injured ahead of the Europa League match at PAOK Salonika.
Thessaloniki Police told ESPN FC that two Chelsea fans got into a fight at around 5 a.m. on Thursday after leaving a bar.
They sustained light injuries and did not go to hospital, so the police took them back to their hotels.
The Associated Press reported that an ambulance crew provided first aid but the men declined to be taken to hospital.
"We are aware of an incident that occurred in Thessaloniki last night," Chelsea said in a brief statement. "The police have also been made aware."
No arrests were made and the police do not have any wider concerns about security around the game.
PAOK host Chelsea later on Thursday in the Europa League.