Three Hull City fans were arrested in clashes before and after their side's Europa League play-off first leg match in Belgium.
The arrests came after Hull City supporters claimed they had been injured by bottles thrown at them by KSC Lokeren fans.
BBC reporter Phil Norton in Lokeren said he had seen a number of supporters with cuts to their head.
Humberside Police said it was investigating with Belgian officers.
Humberside Police said two people were arrested for being drunk and disorderly and one for criminal damage, and said there were clashes before and after the match, which Lokeren won 1-0.
It was reported on the BBC website that Hull City supporter Matthew Rudd said the trouble after the game began as fans were escorted by police away from the stadium.
He said: "There was only one way out and we went past this little pub and there were loads of Lokeren fans in there and they just started hurling bottles at us.
Lokeren's Nill De Pauw (left) and Hull City's Paul McShane Lokeren beat Hull 1-0, with the second leg in Hull still to come
"It was a bit of an experience to be honest and quite intimidating, really."
Craig Harper, who was at the match with his 17-year-old son, said the group of Hull City fans were met by a "cordon of riot police with water cannon pointed at us with dogs".
"It started raining bottles and glasses," he said.
"I looked round to say to my lad 'get down they're chucking stuff at us'.
"I looked at him he's got blood pouring out of his head."
A hospital in Lokeren contacted by the BBC said it could not comment on whether it had treated any football fans for injuries.
Humberside Police said: "The disorder witnessed last night will be taken into account as the return leg approaches and we will police the match accordingly."