“It's crazy. We consider this as attempted murder,” said shocked Hertha team manager Michael Preetz, who revealed that only the driver had been in the bus at the time and had miraculously escaped unscathed.
“Our driver was going from the hotel to the train station at Bielefeld to collect the team,” explained Preetz.
“An unidentified person on a motorbike fired at the bus,” he said, adding that “the type of firearm used has not yet been determined”.
A photo posted by the club on Twitter showed the impact of the bullet which smashed a hole in the windscreen at the level of the driver's head.
Police told SID, an AFP subsidiary, that an investigation was underway, as second-division Bielefeld condemned the attack.
“We're shocked by the attack on the Hertha Berlin bus. Fortunately no Berlin colleague was injured,” the club from North Rhine-Westphalia region of western Germany said on Twitter.
The incident overshadowed the first round of matches where Bayern Munich got their Cup campaign off to a 3-1 winning start over amateur fifth-division side Nöttingen as Bundesliga rivals Hamburg fell at the first hurdle for the second consecutive year.
Hamburg, who open their Bundesliga campaign at champions Bayern next Friday, fell 3-2 after extra time at fourth-division Carl Zeiss Jena.
Hamburg join newly-promoted Ingolstadt, who lost 2-1 at fourth-division Unterhaching, and Hoffenheim, who lost 2-0 at second-division Munich 1860, as the elite victims.
Four days after their 1-0 victory over Real Madrid in the Audi Cup, Bayern overran their amateur rivals, playing at Karlsruhe Stadium.
New Chilean signing Arturo Vidal opened the scoring for Bayern with a penalty after six minutes but ten minutes later Noettingen equalised thanks to striker Niklas Hecht-Zirpel, a young student of sports and mathematics.
Mario Götze put Bayern back in front just a minute later with Robert Lewandowski sealing the winner ten minutes later as Munich coach Pep Guardiola brought on Dutch midfielder Arjen Robben after 55 minutes.
Holders Wolfsburg eased to a 4-1 win at Stuttgarter Kickers, as Borussia Dortmund, last season's runners-up, won 2-0 at Chemnitzer FC with goals from Pierre-Emerick Aubameyang (25) and Henrykh Mkhitaryan (82).
There were wins for top-flight sides Hanover and Mainz who beat fourth-division Kassel 2-0 and Cottbus 3-0 respectively.