ENDING a disappointing spell of form against German visitors who moved into second place in the Bundesliga table at the weekend and trail Bayern Munich by just three points was always going to be a tall order for Celtic.

Yet, the self-inflicted nature of a 4-0 defeat to Bayer Leverkusen that leaves them rooted to bottom spot in Group G and facing an uphill task to secure a place in the last 32 made it a painful evening for the Glasgow giants all the same.

Supporters who had last month hailed Ange Postecoglou for the adventurous and attacking style of play he had introduced as they thrashed Scottish rivals Dundee, St Mirren and Hearts at home, were tonight cursing him at times for his tactical naivety in Europe.

The Greek-Australian’s men, lifted by the return of both Kyogo Furuhashi and Callum McGregor, did well in attack in spells against quality opponents and forced a succession of outstanding saves from Lukas Hradecky. The final scoreline would have been rather different if the Finn had not been on the field.

Celtic were, too, desperately unlucky to fall behind in the first-half. David Turnbull slipped on the sodden turf in his own penalty box and gave the ball away. Gerardo Seoane’s side capitalised on the unforced error ruthlessly.  

However, the second goal the home team conceded was a direct result of the manager insisting that his full-backs push forward. Anthony Ralston was posted missing and they fell further behind as a direct result. Angeball will need to be revised if progress to the knockout rounds is to be secured.

READ MORE: Roger Mitchell gives 'dark days' Celtic verdict as ex-SPL chief reveals doubts over Ange Postecoglou future

The reverse means the Parkhead club have now won just two of their last eight outings. The only teams they have defeated during that wretched run are Ross County and second tier Raith Rovers. Injuries have played their part in the dip in form. Still, adopting less gung-ho approach, on the continent especially, may be advisable in the coming weeks.  

McGregor gave the ball away in a dangerous area just outside the Celtic penalty box with a careless header within seconds of Italian referee Marco Di Belle getting proceedings underway. Kerem Demirbay pounced and got a long-range attempt on target. Joe Hart, though, was untroubled by it.

The keeper was called upon moments later when Florian Wirtz tried his luck from distance. Lucas Alario pounced on the rebound and headed into the net. Linesman Matteo Passeri raised his flag for offside and the goal did not stand. But there were just 56 seconds on the clock. It did not augur well for the rest of the evening.

The Leverkusen rearguard, however, did not look particularly watertight early on either. In the second minute, Furuhashi barged past the two centre backs and rounded Hradecky. Just as he was about to slot into the net, Jonathan Tahslid blocked him with a perfectly-timed challenge. It was a whirlwind start.   

Jeremie Frimpong, the Dutch right back who was sold by Celtic to Leverkusen in an £11m transfer back in January, made his return to the club where he made his breakthrough in the senior game and was once adored by supporters. But the 20-year-old was booed as he broke upfield in the 10th minute and every time he got on the ball thereafter.

He home supporters have new heroes now. Jota, the Portuguese winger who has joined on a season-long loan from Benfica, is well on his way to being one of them. He initiated a slick attacking move in the 15th minute when he sent Adam Montgomery through with a cheeky backheel.

His team mate cut the ball back to Tom Rogic who volleyed over the crossbar.  But the encouraging passage of play lifted the sell-out crowd and the Celtic players. Furuhashi nearly beat Hradecky after being supplied by Liel Abada. The keeper also did well to tip a Carl Starfelt attempt past his right post with his fingertips.  

Leverkusen looked dangerous on the counter attack and Moussa Diabby tested Hart after getting on the end of a long ball upfield. But the opener when it came in the 25th minute was harsh on the home team. Turnbull fell trying to control the ball and Mitchel Bakker took advantage of his misfortune.

He picked out Piero Hincapie with a pass and the Ecuadorian hmade no mistake. Montgomery, selected at left back in the absence of both Josip Juranovic and Greg Taylor, slid in to try and keep it out, but simply succeeded in helping the ball into his own net.  

If the first was unlucky for Celtic the second 10 minutes later was unnecessary and avoidable. Paulinho advanced unchallenged down the left flank in the and then found Wirtz with a diagonal behind Cameron Carter-Vickers and Starfelt. The attacking midfielder, or his side for that matter, will not have scored many easier goals.

Hradecky denied Furuhashi once and Jota twice with instinctive reaction saves as Celtic set about clawing their way back into the game with purpose in the second-half. It must have hurt when they fell three goals behind to a controversial penalty.

Hart palmed a Frimpong effort to the feet of Paulinho and the Brazilian forward rifled a powerful shot at goal. Carter-Vickers slid in and got his body in the way. Di Bello ruled, to the disbelief of the Celtic players and fans, the centre half had handled it. Lucas Alaric coolly converted the spot kick.

Postecoglou threw on James McCarthy, Nir Bitton, Albian Ajeti and Giorgos Giakoumakis, who made his long-awaited debut, for McGregor, Rogic, Furuhashi and Turnbull. But Patrik Schick, scorer of a double for the Czech Republic against Scotland at Hampden in Euro 2020 back in June, came on and nearly made it four.

Amine Adil did so in injury time as Postecoglou pushed men upfield in an attempt to snatch a late consolation goal. Celtic will not face much better than Leverkusen in the coming months. Still, important lessons must be learned if they are to return to winning ways.