Europa League barrel. Ange Postecoglou 's side created a host of chances in front of a packed Parkhead, only to find Lukas Hradecky in impassable form and their strikers wanting for accuracy.
At the other end of the park individual errors saw Leverkusen slice the hosts apart with clinical regularity, Piero Hincapie, Florian Wirtz, Lucas Alario and Amine Adli providing the killer blows.
The 4-0 defeat leaves Celtic bottom of the group ahead of the double-header with Ferencvaros, with the top two already disappearing into the distance.
Beating the Hungarian champions twice would provide a Conference League parachute but, on this evidence, the cream of this competition are a level too far for a team still in the rebuilding process.
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