Germany coach Joachim Loew has branded the bullying of Cologne's Kevin Pezzoni by fans as "unacceptable" after the defender was forced to quit the second division club after being threatened.
"It is unacceptable that this could happen," Loew said ahead of Germany's opening World Cup qualifier against the Faroe Islands on Friday in Hanover.
"We have to seriously consider how to avoid such things happening in the future."
Nearly three years after Germany goalkeeper Robert Enke committed suicide after suffering from depression, there deep concern here after Pezzoni, 23, quit Cologne having been confronted by menacing fans at his home last week.
A group of supporters targeted him by leaving a note on his car, threatening him with violence, then aggressively confronted him at home after organising themselves using the Internet.
Having joined Cologne in 2008 from Blackburn Rovers, Pezzoni, who had his nose broken by a fan in February while celebrating in the city, told club coach Holger Stanislawski he no longer felt safe playing for the team.
Cologne have agreed to Pezzoni's request to have his contract terminated.
Germany's team manager Oliver Bierhoff, who spent a decade playing in the Italian league between 1991 and 2001, said he had witnessed similar things and called for them to be stamped out of football.
"I personally know of situations like this from my time in Italy," said the 44-year-old.
"These aren't fans, they are criminals who have to be watched and pushed out of the sport.
"It is not an easy thing to do, but we should not trivialise the issue and we have to work together to address it.
"Such a thing we don't want to see in the sport, it has nothing to do with football."
Germany midfielder Andre Schuerrle said Pezzoni's desperation to leave Cologne shows things had got out of hand.
"If someone is pushed so far to take such emergency measures, it is certainly a crazy situation," said the Leverkusen star.
Ulf Baranowsky, managing director of Germany's professional footballers union, said he was following the Pezzoni case with "horror".
"If this continues, we will soon have conditions like in Mexico, where players have already been hunted to death. There have also been cases like this in South Africa," he told German daily Bild.
"These aren't isolated incidents.
"Cars are scratched, a player has had his leg broken, another suffered a broken nose in a disco. In Dreden, 11 graves were dug as a threat.
"The inhibition threshhold (of fans) seems to be lowering, while the hysteria grows."