Dutch police said in a statement they had arrested two Legia Warsaw players who had assaulted two AZ Alkmaar staff members "to such an extent that they needed medical attention."
The two players have been widely named as Portuguese midfielder Josue Pesqueira and Serbian centre-back Radovan Pankov.
The confrontation took place when the Dutch police blocked the Legia Warsaw team bus "for the players' own safety" because visiting fans were still being escorted from the ground after the game, which AZ Alkmaar won 1-0.
"A number of players and officials apparently disagreed with this and started to become violent," Dutch police said.
Riot police boarded the bus and took the two players into custody, where they are being investigated for assault.
"An arrest is a serious measure, the police do not do this without reason. Certainly not with players after an international match," the police added.
According to Polish media, the police stormed the bus, pinning club president and owner Dariusz Mioduski to the ground and smashing his mobile phone as he was recording the events.
"What happened is an absolute scandal," Mioduski said, adding that he had experienced rival fans attacking a team bus, but never hosting officials.
"It's a precedent on a global scale... the team is shocked by what happened because no one has experienced anything like this before," he told reporters, visibly shaken.
'It's a game of football'
Violence had broken out even before the match began, according to Dutch police, with Legia Warsaw fans storming the entrance to the ground in the run-up to kick-off and knocking one officer unconscious.
Police deployed tear gas to disperse the visiting fans, who managed to grab batons and pepper spray from the under-pressure authorities.
The Dutch authorities said they had informed the Polish club in advance they would not be able to police the game safely due to other events in the city, asking them to keep fans at home.
"During match day, it became clear that Legia Warsaw had not stuck to this agreement," the police said, saying they "seriously disapproved" of the club's behaviour.
With elections looming in both countries, the spat quickly escalated to the political level.
Polish Prime Minister Mateusz Morawiecki described the events as "very worrying" and called for an urgent probe into the violence, insisting that Polish supporters should be "treated according to law."
Deputy Foreign Minister Pawel Jablonski added that his office was looking into whether "the Dutch police and AZ Alkmaar staff broke the law in relation to Polish citizens... due to their nationality and their use of the Polish language."
The Polish football federation has also asked their Dutch counterparts and UEFA for explanations.
Dutch police insisted that portrayals of the incidents in the Polish press were misleading.
"The Polish media paints the picture that players were victims of riot police actions, but this is by no means the case. It was the players who used violence," they said.
Dutch Justice Minister Dilan Yesilgoz said her main concern was the injured police officer and she lashed out at the travelling fans.
"It's a game of football. So behave and don't lean on the police. The aim is to have fun," she said.
She dismissed the criticism from Morawiecki, saying: "I would prefer he looked at his own club first."
