Ryan Babel has been asked by the German Football Association to explain comments on his Twitter account suggesting a referee was on drugs.
Referee Thorsten Kinhofer dismissed the Hoffenheim forward for two yellow card offences within seconds of each other during a 3-1 defeat to Hertha Berlin on Saturday.
That prompted the 25-year-old Dutchman to claim via Twitter that the "ref was on drugs", sparking the proceedings by the German FA (DFB).
The DFB will hear his explanation of events before deciding whether to hit Babel with an additional suspension to the automatic one-match ban he will receive for the red card.
It is not the first time that the Holland international has angered the authorities with his use of the social networking site.
Babel was fined last year, during his time as a Liverpool player, for posting a photoshopped image of referee Howard Webb in a Manchester United shirt.