One supporter died of a heart attack and another was rushed to hospital during Borussia Dortmund's home match against Mainz on Sunday.
Dortmund claimed a routine 2-0 win thanks to goals from Marco Reus and Shinji Kagawa, but events at Signal Iduna Park were overshadowed by tragic events in the stands.
Much of the game was played out in front of a subdued crowd as news of the heart attacks filtered through, with Dortmund confirming after the game: "There have been two tragic incidents inside the stadium during the game.
"Unfortunately, one of the people did not make it and passed away. We have been informed that the second person's situation is stable.
"Our thoughts are with the victims' families."
Reus, meanwhile, confirmed that the players were unaware of the tragedy until after the final whistle.
"The players did not know anything about what happened and we were a bit annoyed that the entire stadium went silent," the told Sky.
"The coach told us immediately after the game what had happened. All of a sudden this match is no longer important."