Schalke have condemned the behaviour of a group of the club's fans after players and staff were attacked outside their stadium in the early hours of Wednesday morning.
Schalke lost 1-0 at Arminia Bielefeld on Tuesday to confirm their drop into the 2. Bundesliga for the first time in 33 years.
After the game, Schalke travelled back to the Veltins Arena, where they were met by hundreds of angry supporters.
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Eggs were thrown towards the players and staff, while police say flares and fireworks were set off.
A statement from Schalke acknowledged the anger felt by the club's fans over their relegation, but said those outside the stadium had "overstepped boundaries".
The statement read: "There was a brief exchange between the players and some groups of fans after returning from Bielefeld in the early hours of Wednesday morning.
"During the course of the encounter, some currently unidentified individuals overstepped boundaries that are non-negotiable for FC Schalke 04.
"Despite the understandable frustration and anger with our relegation to the Bundesliga 2, the club can never accept the physical endangerment of our players and staff. That is exactly what occurred during last night's confrontation.
"The club strongly condemns this behaviour and stands behind our staff. An investigation into the incident is already underway.
"FC Schalke 04 will give no further comment on this matter until things are cleared up."
Schalke's relegation comes just three years after they finished as runners-up in the Bundesliga, and only two years after they were playing in the knockout stages of the Champions League.
They have endured a wretched season, conceding more goals - 76 - than any Bundesliga side since 2000, and still have four matches left to play.
Schalke are currently managed by Dimitrios Grammozis, who took over in March to become the club's fifth manager of the season.
They began the campaign under former Huddersfield boss David Wagner, but he was sacked in September on the back of an 18-game winless run in the Bundesliga.
Former Tottenham boss Christian Gross took charge in December, despite not having managed in Europe for nearly nine years. He left three months later.