The former Germany international slammed his side's performance against the Red Devils, while Stefan Kiessling feels an attacking approach cost them dearly
The Werkself's proud home record this term came to an abrupt end against David Moyes' side, who triumphed thanks to strikes from Antonio Valencia, Johnny Evans, Chris Smalling, Nani and an Emir Spahic own goal.
The former Germany internaitonal said that losing by such a margin is always humiliating, irrespective of the quality of the opposition.
"To lose 5-0 at home is embarrassing, even if Manchester United are your opponents," Voller told ZDF.
"In the second half, you didn't get the feeling that we could turn things around."
Star striker Stefan Kiessling, meanwhile, believes that his side shot themselves in the foot by adopting a more adventurous approach than they had during the 4-2 loss at Old Trafford in September.
"I didn't think we were as frightened in this game as in the first match against United," the forward said.
"We tried a more footballing approach which worked out until we conceded the goals. Getting shot like we did in the second half is something that cannot happen."
In order to progress to the last 16, Leverkusen must now beat Real Sociedad in their final group game and hope that United do them a favour by denying Shakhtar Donetsk a victory at Old Trafford.