Jens Lehmann is suing Werder Bremen's Tim Wiese for €20,000 after the German goalkeeper suggested he belonged in a mental institution.
Arsenal 'keeper Lehmann took exception to comments Wiese made after Werder Bremen's 2-2 draw with Tottenham Hotspur in the Champions League on September 14.
Lehmann, who was working as a pundit for German television, said Wiese was to blame for one of Spurs' goals, saying: "If he had taken a step out, he would have been able to catch the ball. He should not have stuck himself to the post but rather been more courageous. He can certainly do better."
Wiese, who has endured a strained relationship with Lehmann, hit back in an interview with Bild newspaper, saying Lehmann should "check himself into a clinic - preferably a secure unit."
He added: "He should go on the Muppet Show - that man belongs on the couch. Maybe he could get help there."
Wiese has always claimed Lehmann would not shake his hand before matches and ahead of the World Cup the former Germany international backed Manuel Neuer and Rene Adler for Die Mannschaft's No.1 Jersey ahead of the Werder keeper.
The case will be heard in Munich's State Prosecution Court on Thursday. Neither Lehmann nor Wiese will be required to attend the hearing, when it will be established whether or not Wiese's remarks were defamatory.