The suspect, identified only as Alaa S. under Germany's privacy laws, stabbed the man during a quarrel in the eastern city of Chemnitz.
German authorities did not say if the suspects were involved in the wave of xenophobic marches that swept Chemnitz at the end of August following a fatal stabbing, allegedly by an asylum seeker.
Saxony state, where Chemnitz is located, has been a stronghold of far-right parties and groups that bitterly oppose Chancellor Angela Merkel for her 2015 decision to keep open German borders to a mass influx of migrants and refugees.
Many Germans were alarmed by images distributed on social media of skinheads performing the Hitler salute during the protests in Chemnitz.
After a weekend of protests in which right-wing extremists vastly outnumbered counter-protesters, a huge crowd estimated by city authorities as 50,000 people massed at the Chemnitz free concert Monday.
In all, 18 people were injured, including three police officers, said in a statement Sunday, doubling their earlier injury estimate.
Bono appeared to have a problem with his voice after the first few songs - the 58-year-old stopped singing to drink from a thermos flask.
The incident occurred days after the violent protests in the eastern city of Chemnitz that were triggered by the fatal stabbing of a German man there.
Some carried banners or insignia of the far-right AfD and neo-Nazi NPD parties and other extremist groups, while a handful delivered the illegal right-handed Hitler salute.