The player, Henrikh Mkhitaryan, is a member of the national team of Armenia, which technically remains at war with Azerbaijan over the region of Nagorno-Karabakh. Because of those political tensions, Mkhitaryan feared visa problems or — at worst — being arrested as soon as he set foot in Azerbaijan.

Despite assurances from Azerbaijan’s foreign ministry and pledges of support from European soccer’s governing body, UEFA, Dortmund decided safety concerns left it no choice but to avoid the risk completely.

"Based on the situation,” Mkhitaryan’s teammate Roman Weidenfeller said this week, "it is better to leave Henrikh at home.”

And Dortmund could face another situation similar to Mkhitaryan’s in the near future: Another of its players, Adnan Januzaj, received death threats last year after he announced that he would play internationally for Belgium instead of Kosovo or Serbia, which he was also eligible to represent. News media reports in Belgium and Serbia at the time said the 20-year-old Januzaj was warned never to set foot in Balkan territory again.

Several Balkan teams remain alive in the Europa League, as does Dortmund, which moved into first place in its group with its win over Qabala.

"It’s a region of crisis,” Dortmund’s chief executive, Hans-Joachim Watzke, said Wednesday before the trip to Baku. "Especially the relationship between these two nations. We spoke to Henrik, and we think it’s best for everyone.”

"He felt somewhat uncomfortable in the situation,” Watzke added. "This is the best solution for all sides.”

And Dortmund could face another situation similar to Mkhitaryan’s in the near future: Another of its players, Adnan Januzaj, received death threats last year after he announced that he would play internationally for Belgium instead of Kosovo or Serbia, which he was also eligible to represent. News media reports in Belgium and Serbia at the time said the 20-year-old Januzaj was warned never to set foot in Balkan territory again.

Several Balkan teams remain alive in the Europa League, as does Dortmund, which moved into first place in its group with its win over Qabala.

"It’s a region of crisis,” Dortmund’s chief executive, Hans-Joachim Watzke, said Wednesday before the trip to Baku. "Especially the relationship between these two nations. We spoke to Henrik, and we think it’s best for everyone.”

"He felt somewhat uncomfortable in the situation,” Watzke added. "This is the best solution for all sides.”

The decision robbed Dortmund of one of its most dangerous attackers; Mkhitaryan has 10 goals and eight assists in 16 appearances this season.

Moments before Thursday’s game, Mkhitaryan posted a photo of the match on Twitter with a simple message: "Didn’t travel with our boys, but will support from home!” He also posted his congratulations to Dortmund’s players on their victory shortly after the final whistle.

It was not the first time a big club had made an unusual roster decision for a game in Eastern Europe. Last season, Tottenham Hotspur left five black players at home for an important game at Partizan Belgrade. Tottenham’s manager, Mauricio Pochettino, said the choices were made only for "footballing reasons,” but few English fans had forgotten the racist chants and physical abuse that rained on one of the players, defender Danny Rose, when he played for England in the country two years earlier.

Racism did rear its head at one match this week. On Thursday, UEFA said that it would open disciplinary proceedings against Dynamo Kiev after four black fans were attacked in the club’s stadium during a Champions League match against Chelsea on Tuesday.

Video of the attack was posted to YouTube and broadcast widely in the European news media; it shows Dynamo fans attacking the four men, who were forced to try to escape with little or no help from stadium security officials. The antidiscrimination group Football Against Racism in Europe (FARE), which tracks racism in European soccer, said it had sent an observer report to UEFA on the incident.