Anti-discrimination group Fare Network says there is "a very high risk" of crowd trouble when Ukraine face Kosovo in a World Cup qualifier on Sunday in Poland.
Far-right fan groups in several Eastern European countries are strongly opposed to Kosovo's participation and claim the tiny Balkan nation is rightfully part of neighboring Serbia.
This year has also seen increasing political tensions between Poland and Ukraine, accompanied by the release this week of a film dramatising the massacre of ethnic Poles by Ukrainian insurgents during World War II.
Ukraine is technically the home side, but Sunday's game is being played in the Polish city of Krakow because Ukraine's government does not recognise Kosovo as an independent state. While Polish authorities have reportedly restricted the number of fans inside the stadium to around 1,000, there are indications that more may travel to Krakow, where local clubs Wisla and Cracovia have a long record of hooliganism.
"FIFA say the numbers are restricted but we won't know how far that has been enforced until the game itself. Inside and outside the stadium, the match poses a very high risk," Fare's executive director, Piara Powar, told The Associated Press. "The last thing Europe at the moment [needs] are huge displays of this kind of aggressive nationalism."
Krakow police spokesman Dariusz Lach told the AP that no extra security measures would be in place for the game.
"This will not be a mass event," he said. "Right now we don't expect any problems during the match and we are not taking any special measures."
There is confusion over how many Ukraine and Kosovo fans plan to attend. Ukrainian Football Federation spokesman Mykola Vasilkov suggested the 1,000 fans allowed inside the stadium only applied to Ukrainian supporters.
However, Kosovo Football Federation spokesman Fazli Berisha said that, while supporters living in Kosovo would be deterred by the need for a visa, "we believe we shall be supported by our brethren living in other European countries."
Kosovo became a UEFA member in May, joined FIFA a week later and were fast-tracked into 2018 World Cup qualifying. They earned a point in a 1-1 draw with Finland in their first competitive fixture but lost 6-0 to Croatia on Thursday in a game marred by anti-Serbian chants by both Kosovan and Croatian fans.
Ukraine drew their opening two games against Iceland and Turkey.