Police said on Tuesday that Hells Angels bikers tried to storm a club whose bouncer was connected to their sworn enemies, the Bandidos.
The shots appear to have been fired by someone inside the club, and wounded one of the Hells Angels as well as the passer-by.
Now police are searching for a 40-year-old bouncer on suspicion of attempted murder, but he has gone to ground. The weapon used has also disappeared.
Fearing reprisals by the Hells Angels, around 150 officers were deployed around central Düsseldorf and 46 restraining orders issued banning suspected bikers from the area over the weekend.
Police also noted that two men, one of them a Hells Angels biker, were stabbed in nearby Oberhausen on New Year's Eve.
They fear that a gang war may be set off by an increased number of Bandidos moving from the Ruhr region, their traditional stronghold, into the Rhineland, which the Hells Angels see as their territory.