Celtic have been defeated 7-1 by Borussia Dortmund in their second UEFA Champions League game.
Karim Adeyemi scored a first-half hat-trick to add to penalty kicks from Emre Can and Serhou Guirassy with Daizen Maeda scoring for the visitors.
Guirassy scored his second of the game after the hour mark before substitute Felix Nmecha finished the scoring with ten minutes to go.
Brendan Rodgers' side won their opening match of the competition 5-1 against Slovan Bratislava.