Fans of third-division Rot-Weiss Essen have sealed the away entrance with concrete, hours before Tuesday's home German Cup match with RB Leipzig.
AFP subsidiary SID reported on Tuesday that "unknown perpetrators had sealed the entrance to the away section in the stadium with concrete" late on Monday night.
Above the fresh concrete was a message reading "bulls must stay out" in a clear attempt to stop away fans from attending the match.
City officials were seen trying to remove the concrete on Tuesday afternoon, hours out from the 6pm kick-off time.
Owned by energy drink giant Red Bull, RB Leipzig are unpopular with many fans in Germany, where clubs are generally owned and run by members.
Supporters of other clubs have held up banners criticising the club's ownership model, while in 2024, the away section of Bundesliga club Heidenheim was sprayed with butyric acid to produce a vomit-like smell ahead of a match with the Saxon club.
First promoted in 2016, RB Leipzig have won the German Cup twice. They made it to the semifinals of the Champions League in 2020.