The German FA (DFB) has told ESPN FC that it has opened an investigation after Borussia Dortmund's Jadon Sancho was hit by a lighter thrown from the stands during the 4-2 home defeat to Schalke on Saturday.
England international Sancho and his teammates were celebrating near the travelling Schalke fans after BVB took a 14th-minute lead when he was hit and needed treatment for a minor head injury.
Dortmund police have filed charges against an "unknown perpetrator who threw a lighter at Jadon Sancho from Schalke's stand," authorities told ESPN FC.
As Sancho was being treated, Schalke began a move that ended with them being awarded a penalty by a VAR review, but Dortmund have said they will not appeal against the result and it will stand.
The DFB is now set to punish Schalke for the behaviour of their fans, who displayed a banner calling for the release of Sergej W, the man sentenced to prison for the bomb attack on Dortmund's team bus in 2017, and also used pyrotechnics.
Former Dortmund player Marc Bartra, injured in the bus attack, called the banner "intolerable" on Twitter, writing: "Rivalry might be one thing, but demanding freedom for someone who tried to take the life of 28 people is another thing."
Schalke have apologised for the "distasteful display," telling ESPN FC they "reserve the right to take further steps against those displaying the banner."
Dortmund fans are also under scrutiny for a banner with an anti-gay slogan directed at Schalke fans, while both clubs could face consequences after supporters clashed following the final whistle.
Meanwhile, the DFB has banned Dortmund captain Marco Reus for two games following his red card on Saturday.