Paul Lambert is still revered at the Westfalion Stadion after helping Borussia Dortmund win the Champions League in 1987, winning the Man of the Match award in the final after marking Juventus playmaker Zinedine Zidane out of the game as the underdogs beat the holders 3-1.

His time in the Bundesliga sparked a lifelong love affair with German football and he has always kept up to speed with developments there. Indeed, he’s spent the last few weeks traversing the country, taking in matches and visiting old friends to soak up information and ideas for when he returns to management following his decision to step down at Ipswich Town on March 1.

During his travels he has been impressed by Bayer Leverkusen, who face Celtic at Parkhead on Thursday night. It is only the second round of fixtures in Group F of the Europa League but Lambert fears that a defeat to a team he claims is capable of going on to win the trophy could hole the hosts below the waterline.

After surrendering a two-goal lead ton lose 4-3 to Real Betis in Seville, Lambert argues that there is no wriggle room for his former club if they are to remain in UEFA’s secondary competition.

“This isn’t a must-win game for Celtic but, after being beaten by Real Betis in Seville, it’s definitely a must-not lose game,” he said. “The crowd can help Celtic a lot: I know from personal experience that they can make the difference in big European nights. Anything is possible in a one-off tie but Leverkusen are a very good side.

“It’s also not in their nature to come to Glasgow for a draw: that’s just not the way they play. They’ll come to win and the worst thing that could happen to Celtic is that they lose and Betis beat Ferencvaros in Hungary because then they’d be six points behind the pair of them and battling Ferencvaros – who put them out of the Champions League last year –  to finish third and drop into the Conference League.

“I know that Ange Postecogloou likes his team to play on the front foot but they’ll need to watch out because Leverkusen have pace to burn in their ranks and they’re very quick on the counter. Celtic’s home form has been pretty good, though, and I hope that continues.

“I don’t expect Postecoglou to change his style and nor should he – he’s come to Celtic when they’re going through a rough time and he needs to stick to his beliefs. I think he’s grasped what the club is and what it means to people and he’s handled the situation really well.”

Like the Australian, Swiss coach Gerardo Seoane is in his first season at the BayArena but he has enjoyed a more productive start to his tenure.

“I don’t know him personally but he’s done really well, winning three titles in a row with Young Boys and also lifting the Swiss Cup with them for the first time in 33 years,” Lambert added. “He’s only 42 and he moved to Leverkusen in the summer. The only setback for him so far has been a 4-3 defeat against Borussia Dortmund – and, even then, not many teams score three against my old club.

“They won 4-1 away to Ausburg a few weeks ago and I was at that one. They played a 4-2-3-1 formation and the front four were outstanding. That includes their star man, Florian Wirtz, who’s one of the best young midfielders in Europe.

“I saw him making his debut as a 16-year-old and thought: ‘I’ll need to keep an eye on him.’ Now he’s 18 and playing for the German national team. He has a little bit of everything; he can tackle, dribble, pass and shoot – he’s scored a few times when I’ve seen him, including a great goal in that game against Ausburg.

“He’s equally effective as an attacking player or a holding midfielder and I’ve absolutely no doubt that he’s going to be a star. Then there’s Moussa Diaby, the winger who’s made his first appearances for France this season – he’s 22 and lightning quick. He’s also a really clever footballer.”
A more familiar foe is towering target man Patrik Shick, the hammer of the Scots at Hampden in June.

“He scored four goals at the Euros, including two against us,” said Lambert.

“He holds the ball up well and he also scored with a spectacular 20-yarder in that game at Augsburg so he’s a real threat. He’s a big, strong lad at 6’ 3” but, as we’ve seen, he’s excellent with the ball at his feet so Leverkusen don’t launch high balls at him – that’s just not the way they play.

“Perhaps the biggest danger, though, is another midfielder, Kerem Demirbay, who’s a good technical player with a great left foot. He was signed for a club record £32m from Hoffenheim two years ago but is only really now playing at his best under Seoane. They also need to look out for Charles Aranguiz, a crafty little Chilean playmaker who can pick passes and score as well.

“Celtic fans know all about Jeremie Frimpong. He’s done well since his move, especially going forward. Celtic couldn’t turn down £11m for him and Leverkusen have a great reputation for developing young players and selling them on for big money, like they did with Kai Havertz to Chelsea and Leon Bailey to Aston Villa. But Wirtz is the one for me: he’s a player who can hurt you.

“But this is as good a team as Celtic will face this season, good enough to reach the final and even win the competition. Honestly, Celtic will need to be right at the top of their game to keep up with them.”