Five people have been arrested after a Manchester City fan was attacked while travelling home from Tuesday's Champions League game against Club Brugge.
The Belgium-based supporter was attacked at a service station on the E40 motorway in Drongen.
He was taken to a hospital in Ghent.
Man City said they were "shocked and saddened" by the incident, while Club Brugge said they were "horrified".
A statement from the East Flanders public prosecutor said: "A man wearing a Manchester City scarf had stopped his car at the highway parking in Drongen after the match and had gone to the shop.
"According to the first findings of the investigation, his football scarf was taken in the shop by a suspect and he walked outside with it. Subsequently, the victim came into confrontation with some suspects in the parking lot, and ended up on the ground after physical aggression.
"The emergency services arrived on the scene. The victim, a 63-year-old man from Ninove, was taken to hospital. He is in mortal danger.
"Due to these facts, the police arrested five people during the night."
Manchester City said they were working with Club Brugge as well as Belgian and Greater Manchester Police to establish more information.
A City statement said: "Our thoughts and best wishes go out to the family and friends of the Belgian-based supporter, who remains in hospital."
Brugge added: "Club Brugge was horrified to learn of the events at the E40 motorway parking lot in Drongen where a Manchester City supporter, who had previously been a guest at the Jan Breydel Stadium, was attacked.
"Club Brugge strongly disapproves of all criminal behaviour, both inside and outside the stadium and puts tolerance first. Our thoughts go out to the family and friends of the Manchester City supporter."
Manchester City were 5-1 victors at the Jan Breydel Stadium.