The incident occurred following a league match.
Barton, 37, is alleged to have pushed the German boss at Barnsley's Oakwell Stadium on April 13 this year, leaving him with a damaged tooth.
The former England international pleaded not guilty to a charge of assault occasioning actual bodily harm when he appeared at Sheffield Crown Court on Wednesday.
A provisional trial date was fixed for June 1 2020, reports the Mirror.
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