Four Euro 2012 stewards were attacked by Russian football supporters after the country's 4-1 win against the Czech Republic, police in Wroclaw, western Poland, said on Saturday.
An amateur video broadcast by the Polish television channel TVN24 appeared to show a group of supporters punching and kicking the volunteers, who were wearing the distinctive green tabards and positioned in the stadium for the tie on Friday.
"Four people were hospitalised for a short time following this incident," Wroclaw police spokesman Pawel Petrykowski confirmed. "We are trying to identify their attackers."
European football's governing body UEFA said in a separate statement that it was aware of a "brief and isolated incident involving a small group of around 30 fans who attacked a handful of stewards.
"The situation was quickly and efficiently brought under control. The local police are aware of the incident and investigating.
"The cause of the incident is not currently known but we are studying the security reports and available images. UEFA remains entirely committed to the safety and security of all fans and spectators at all matches of Euro 2012."
Just before the same match, police arrested four Russian supporters who had allegedly started a bar brawl in Wroclaw old town. Petrykowski said the four were drunk and had been questioned about the incident.
Warsaw mayor's office last week gave the go-ahead for Russian fans to march in the capital on their national day on Tuesday, which also happens to be the day when their team plays Poland in the capital.
The decision came amid speculation that clashes might erupt between the countries' fans during the 16-nation, quadrennial football showcase, which is being co-hosted by Poland and Ukraine in June.
Poland and Russia have long had a fraught relationship, mired in centuries of conflict, and President Vladimir Putin's present-day Russia elicits aversion from many Poles.
This tension, along with a reputation for violent fans in both nations, has fuelled speculation of possible unrest on the sidelines of the tournament.