A violent group of Barcelona fans could cause more serious trouble unless measures are taken to bring them under control, the Primera Liga club's president Joan Laporta said on Wednesday.
"We have to talk less and act more," Laporta said at a book presentation in Barcelona.
"Either we take steps to prevent them from travelling and getting into the stadiums or we'll see more serious incidents. We will continue to act with the same forcefulness and we will make no concessions to the aggressors."
A club security guard was punched in the face on Tuesday by a fan, widely reported by local media to be a member of the group, at the German hotel where players and staff were staying for the Champions League quarter-final against Bayern Munich.
A Munich police spokesman said on Wednesday that five supporters had been detained until after the match but the fan who threw the punch was still at large. The security guard had not been seriously hurt, he added.
In his time as president, Laporta has stopped the practice of giving the Boixos Nois group free tickets to matches and discount trips to away games and ordered the closure of the room in the Nou Camp where they stored banners.
Laporta, who has received death threats from the group, said the club knew the identity of its members and was drawing up plans to prevent them travelling to away matches and gaining access to stadiums.
The Boixos Nois were blamed for flare-throwing incidents at Barca's match at city rivals Espanyol in October when the referee was forced to halt play for almost 10 minutes and take the players off the field in the second half.
"These individuals continue to present a deplorable image that is neither that of Barcelona nor the vast majority of its fans, whose behaviour yesterday was model," said Laporta, whose team sealed a Champions League semi-final spot with a 5-1 aggregate victory over Bayern.
"The majority of fans who were in Munich behaved exquisitely except these criminals who dedicate themselves only to giving a beating to lads trying to do their jobs."