The German Football Federation (DFB) on Wednesday launched an investigation into Hertha Berlin's relegation play-off defeat at Duesseldorf as crowd trouble left players fearing for their lives.
Fortuna Duesseldorf's 2-2 home draw on Tuesday saw them win the German league relegation play-off 4-3 on aggregate and earn promotion to the Bundesliga at Hertha's expense amidst chaotic scenes.
The relegation play-off clash at Fortuna's Espirit Arena was twice interrupted by pitch invasions as fans fired flares onto the field.
"With dismay and concern, we have noted the incidents in Duesseldorf," wrote DFB president Wolfgang Niersbach and German league (DFL) boss Rainhard Rauball in a joint statement.
"DFB and DFL agree that such irresponsible and threatening scenes in a football stadium can not be tolerated and must be punished rigorously.
"The DFB's disciplinary committee are responsible for finding the appropriate sanction, the Control Committee has already started the investigation."
Hertha, whose players were reluctant to return to the pitch after a mass invasion by fans late in stoppage time, have said they are considering appealing against the result and requesting a replay.
"The players were extremely afraid and were very pale in the dressing room," Hertha's lawyer Christoph Schickhardt told German Sky Sports News.
"It is written in the rules: if there is an outside influence, which has nothing to do with the game, then the match must be replayed."
Having won the first-leg 2-1 in Berlin, Tuesday's return leg was briefly halted after Fortuna took a 2-1 lead with an hour played as dozens of lit flares landed on the pitch prompting referee Wolfgang Stark to stop play.
There was then a 20-minute delay when fans poured onto the field with two minutes of stoppage time still to play as Stark again halted the match before the remaining 90 seconds were finally played out.