Strong security measures were imposed for a soccer match in Belgrade on November 2 in which Serbian team Partizan played Albanian club Skenderbeu.
Both teams are in the same Group B of UEFA's Europa League competition.
Partizan defeated Skenderbeu 2-0 in the match, which was played without Albanian fans as both teams and UEFA had agreed not to allow them to go to Belgrade.
The same rule was applied on October 19 when Serbian fans were not allowed to attend a Partizan match with Skenderbeu at Albania's Elbasan Arena stadium.
To enforce the restrictions, fans had to show their identity cards when they were buying tickets, and they had to sit in places that were listed on their reservation.
Partizan in a statement urged its fans to "cheer fairly" and without "chauvinistic messages." Partizan also warned fans not to "scandalize opponents on a national basis" and "not to express anger and hatred."
The club said that "another incident could cost the club a lot," and it could even be "kicked out of European competitions."
Tension between Serb and Albanian sports fans remains high, reflecting broader political tensions in the Balkans.
An especially hot dispute lingers over the mainly ethnic-Albanian former Serbian province of Kosovo, which declared independence in a move recognized by most countries outside of Serbia.
In an incident that raised tensions in October 2014, a drone carrying a "Greater Albania" flag flew over the pitch during a match between the Serbian and Albanian national teams.