Assistant referee Christian Gittelmann was struck by a projectile from the crowd in Bundesliga on Friday, forcing an abandonment between Bochum and Borussia Monchengladbach.

With Gladbach up 2-0 in the 77th minute, after goals from Alassane Plea and Breel Embolo, Gittelmann was hit in the back of the head by a beer thrown from the crowd.

Bochum had posted an announcement hours before the game on social media, advising fans not to throw beer from the stands.

The club again used social media after incident, this time to issue an apology.

"We can only formally apologise to linesman Christian Gittelmann," a tweet from Bochum said. "A highly embarrassing and bitter evening for us. An extremely stupid action from an idiotic fan."

The match was promptly abandoned after the incident, with the Bundesliga to release further details.