Police chiefs have deployed snipers at England's UEFA Nations League semi-final against Holland after the crowd trouble ahead of the game.
The Football Association called the fans involved in disturbances in Porto on Wednesday night an "embarrassment" to the England team.
The condemnation has been echoed by the National Police Chiefs' Council (NPCC) football policing lead who declared the loutish, stag-do minority are threatening to ruin the Nations League for everyone.
Instead of focusing on Thursday's semi-final with Holland, the build-up is being dominated by fan behaviour after another night of disruption in Porto.
England supporters clashed with Portuguese police and were seen hurling bottles, prompting some local families watching the hosts' match against Switzerland in a fan zone to flee with their crying children.
'England 'til I die' filled the air along with more unsavoury chants - just the latest embarrassing chapter when the Three Lions travel abroad, with trouble marring last year's trips to Amsterdam and Seville.
An FA spokesperson said: "The FA strongly condemns the scenes witnessed in Porto overnight.
"Anyone responsible for these disturbances cannot be seen as true England supporters and are not welcome in football.
"They are an embarrassment to the team and the thousands of well-behaved fans who follow England in the right way.
"We are liaising with the UK Football Policing Unit."
Those issues meant attention turned to Guimaraes on Thursday, with around 20,000 English fans expected at the 26,000-capacity Estadio D. Afonso Henriques.
Supporters were seen lugging crates of beer through the city centre at lunchtime as many locals watched on as the main square was taken over by flags and fans.
Although heavy rain may take the edge off proceedings in Guimaraes, there are fears of trouble over the coming days given England will not be in action again until Sunday.
