Hooligans nailed a banner to the house of Sweden coach Lars Lagerback early Monday, police said.
The banner said: "Resign Lars!"
A group of young men - wearing hoods and scarves to cover their faces - entered the yard of Lagerback's house in a Stockholm suburb and nailed the banner to an outside wall.
The men left before police arrived at 3:45 a.m. (0145 GMT), police spokesman Lars Akerlund said. He did not know how many people were involved in the incident.
"You can have that opinion - that he should resign - but you can't nail it to his house," Akerlund said. "His family shouldn't have to be attacked for the choices he has made."
Lagerback said he and his family slept through the incident, and rejected media reports that the hooligans had broken a window by throwing flower pots and rocks at the house, the AP says.
"We have not experienced anything threatening," Lagerback said in a statement on the Swedish Football Association's Web site. "No window was broken and no rocks were thrown."
The coach has come under fire from Swedish fans and media after two disappointing performances against Germany.
Germany knocked Sweden out of the World Cup with a 2-0 second-round win, and again beat the Swedes in a 3-0 friendly last week.