The German side ran out 4-0 winners at Parkhead, a result which leaves Ange Postecoglou's men bottom of their group after two defeats in two.
Celtic created plenty of good openings but came up against an inspired Lukáš Hrádecký in the Leverkusen goal making a number of excellent saves. At the other end of the pitch, however, it was a different story as the home side gifted the German side two first-half goals.
Bayer added two more after half-time despite a spirited performance at times.
So, how did the players involved rate out of ten.
Player ratings scale - 10: One of the best performances you've seen. 9: Outstanding. 8: Very good. 7: Good. 6: Average. 5: Poor, 4: Very poor. 3: A terrible day at the office. 2: Abysmal. 1: One of the worst performances you've seen.
Bayer added two more after half-time despite a spirited performance at times.