Depending what happens in the other Group G match between Real Betis and Ferencvaros, the Hoops are likely to require a win in Germany to keep their hopes alive of qualifying for the knockout phase on Thursday.

Postecoglou knows it is a formidable test against opponents who won 4-0 at Celtic Park almost two months ago, but with his team unbeaten in nine matches since then, the bullish Australian has no intention of adopting a safety-first mindset.

"We'll only learn from the game if we play our football. You'll learn absolutely nothing if you go out there and shy away from it,"said Postecoglou.

"We can go and be conservative, try and hold on, try and survive, but if we do that we'll learn nothing.

"The only way we'll learn anything in this game is if we go out there and take the game to them. That may be a painful lesson for us all but ultimately it's a better way for us to find out.

"It may not be a painful lesson, it may show that we're making a hell of a lot of progress.

I'd rather go there and find out about ourselves than just go there and try to survive."

Leverkusen have recently snapped out of a five-game run without a win and currently sit fourth in the German Bundesliga.

Postecoglou expects this to be his side's toughest test since he became Celtic manager in the summer.

He said: "It will be a good challenge. They're a good side. They've picked up their form in the league and are going well. We've played against them already so we know the quality of side we're facing."

Postecoglou has no fresh injuries to contend with, but Carl Starfelt, Giorgos Giakoumakis and Socceroo Tom Rogic remain on the sidelines.

Australian Associated Press