Former Hamburg Dynamo Dresden defender Toni Leistner climbed into the stands to confront fans of his old club after the German Cup defeat.
In a video widely shared on social media, the former QPR player, 30, pushes a Dresden fan and argues with others before returning to the pitch.
Toni Leistner was waiting to do a television interview when the incident occurred.
About 10,000 fans watched the game in Dresden – the biggest attendance in Germany since the coronavirus lockdown.
The Dresden-born player, who played for his hometown club between 2010 and 2014, later said he had been insulted by a supporter.
Dynamo have since condemned the supporter allegedly involved, saying it is “shameful” Leistner had been offended by a fan of his “home club”.
“We’re looking for the person because we don’t want to let this incident stand,” the club tweeted.
“Thanks to 99.9% of all stadium visitors for your support.”