Fans of Belgian football club Standard Liege can expect heavy sanctions after a huge banner was unfurled in Sunday's home clash against Anderlecht depicting the severed head of their former captain, who now plays for their bitter rivals.
The banner, raised in a prominent position behind the goal, showed the head of Steven Defour being held by Jason Voorhees, the murderous antagonist of the "Friday the 13th" horror movie series.
Next to the image, fans had written "Red or Dead".
Belgian international Defour transferred from Standard to Porto in 2011 before joining Anderlecht last August in a club record $6.75m move.
"We're working together with police to catch as many of the authors of this banner as possible," a spokeswoman for the interior ministry said on Monday.
She added that individuals faced fines of up to 5,000 euros and could be banned from the stadium for up to five years.
Politicians also voiced their anger over the banner.
"The banner... was in bad taste, it was stupid and unacceptable," Belgian Foreign Minister Didier Reynders tweeted.
Fellow Standard supporter and former prime minister Yves Leterme also expressed his disappointment.
"Standard-Anderlecht has been ruined by a minority of supporters. I remain a supporter but feel ashamed by the banner tonight," Leterme wrote on Twitter.
Standard Liege were not immediately available for comment, while a FIFA spokesperson told Al Jazeera that it was a matter for the local body to look into.