GRONINGEN, Apr 14 (SW) - The toilet paper rolls set on fire by so-called FC Groningen supporters ahead of the home match with Ajax Amsterdam on Sunday, may have serious consequences for the club.

The match had to be postponed to next Wednesday as smoke made it impossible for players to do their work.

When the players arrived to the pitch to begin their important clash, fans from stand 'Z' threw down rolls of toilet paper, which were then set on fire by others.

The initial idea was mentioned to FC Groningen and the local fire department, who both gave their go-ahead.

It turned out that the water extinguisher stadium officials tried to use to put out the fires, lacked pressure and turned out to be useless. Several chairs ended up melted and about 20 fans were treated in clinics or hospital. Four had to stay overnight.

Although the city of Groningen announced to be investigating video footage of those who started the fires, this might not be enough for the Royal Dutch Football Association (KNVB).

"As opposed to what has been said by several media, this doesn't mean that what happened will remain unpunished," said a KNVB statement.

The professional football prosecutor will be launching an investigation which is to decide whether there will be consequences. All parties involved have been asked to make a declaration.