Fans attending Tuesday’s World Cup qualifier between Iran and South Korea in Tehran have been asked to replace football chants with religious slogans, because the match is on a holy day.
Black flags will be raised in the Azadi Stadium and some terraces will be set aside for bussed-in crowds of mourners.
The match at 15:45 BST, is being held on the first of two mourning days on the Shia Islam calendar.
South Korea will wear black armbands as a sign of respect for the hosts.
Some clergymen have said it would be better for Iran to forfeit the game, but it has been decided mourning will take place at the 100,000-seat stadium.
Meanwhile, Iranian officials have complained after the captain of South Korea likened Tehran to a big prison.
Swansea midfielder Ki Sung-yueng also said some Iranian fans threw bottles and other missiles at his team-mates when they arrived in Tehran wearing air pollution face masks.