FC Schalke midfielder Jermaine Jones is being investigated for stamping on the foot of Borussia Monchengladbach star Marco Reus.
The USA international appeared to step on the specially designed boot of Reus, which he was wearing to protect a foot injury, in Wednesday's DFB Pokal clash but the incident was not noticed by the referee.
However, the German football association (DFB) have opened an investigation into Jones who was sent off later in the 3-1 loss because of an unrelated incident.