It is understood the Bayern fans were escorted by police to Karaiskakis Stadium in Piraeus, Greece to avoid clashes with Olympiacos fans.
It is still unclear what provoked the police to become so violent towards the travelling fans. One photo did show a police being struck by seat but it is unknown if this was before or after the police became violent.
The Daily Mail reported that one fan was seriously injured and a club spokesman said: "There was unnecessary loutish behaviour from our fans and disproportionate use of the baton by police".