Celtic need to "keep persevering" with their approach despite Bayer Leverkusen inflicting another chastening loss, says manager Ange Postecoglou.

The German side left Celtic Park with a 4-0 win to inflict a fifth defeat in eight games on Celtic.

Postecoglou's side have lost both of their Europa League group matches, conceding eight goals, while they lie sixth in the Scottish Premiership.

"It shouldn't have been a 4-0 game," the Celtic boss told BT Sport.

"We've got to have a stronger mentality towards the end of the game. Losing a fourth goal was completely unnecessary.

"We've got to keep persevering. We've had a number of injuries, we've had to rebuild the squad, it's not surprising it's taking time. But, within all that, it should be better."

Celtic started brightly against Leverkusen and had numerous chances, but were again fragile when losing the ball as the Bundesliga side put in a ruthless attacking display.

Asked if he would stick to his attacking approach against sides like Leverkusen, the Celtic boss added: "Yeah I don't see any reason why not to.

"They're a quality team and there's always the possibility you'll get punished. But we created enough opportunities to do our own damage tonight.

"We're not going to change our approach. I believe in big games we should go into them and not fear anyone. The process takes time and you're going to cop some knocks on the chin.

"But that doesn't mean you need to accept it. That's avoidable if you do certain things. There were times tonight when we just lost our discipline."

Captain Callum McGregor - who returned to the starting XI after injury - says the squad have bought into Postecoglou's style despite recent results.

"It's a very, very high-demanding style of football," McGregor told BT Sport.

"It takes time for the players to understand where to move and when to move.

"In the defensive transition is where we have struggled. Everyone is together and everyone believes in what the manager is trying to do."