Borussia Dortmund say they will not tolerate incidents like Saturday’s, when supporters broke coronavirus rules to celebrate their 4-0 derby win over Schalke in the Bundesliga.
Erling Haaland's double and goals from Jadon Sancho and Raphael Guerreiro earned the victory, which fans were not able to attend.
Midfielder Mahmoud Dahoud filmed an Instagram Live of up to 200 supporters gathering at the club’s training ground, setting off flares and gathering outside the team bus, ignoring social distancing guidelines and the requirement to wear a face covering.
The video is no longer available on Dahoud’s Instagram account, but was captured and posted on YouTube.
Dortmund have apologised and have vowed to work with police to identify the individuals involved.
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"With all the understandable joy of winning the derby, there were public violations of the coronavirus rules during the team's return to the training ground last night, which will not be tolerated," said a club statement.
"Around 150-200 fans cheered the team outside the training ground, some of whom were not wearing masks and observing social distancing guidelines. Players celebrated with the fans - without leaving the bus - and in the exuberance some even filmed it.
"We can only apologise and promise to talk to the police and all those involved very soon about how such scenes can be completely ruled out in public in future."
Dortmund’s result leaves them sixth in the table, six points off the Champions League qualification places.