Celtic: What lessons can Postecoglou's men take from Europa League exit?

After Celtic's rollercoaster Europa League journey ended with a steep descent to the exit, and the worst defensive record in the group stage, are there positives amid the pain?

A third defeat in five sealed Celtic's fate. From 2-1 up away to Bayer Leverkusen, with a first-ever win on German soil in their grasp, Ange Postecoglou's men were overpowered late on by the slick Germans.

The Australian says there is a "gap between us and the best" and admitted his side are not yet at Leverkusen's level.

"We hung in there, gave ourselves a chance to pull off a great result but ultimately they're a good team," he said.

"They knocked us off 4-0 at home but we gave them a bit of a fright here. Hopefully next time the gap's even smaller."

Porous defence & lack of depth

The numbers are stark and Celtic have conceded the most goals - 13 - in the 32-team Europa League group stage. Only three other clubs - Ferencvaros, who prop up Celtic's section, Royal Antwerp and Legia Warsaw - are into double figures.

On their travels Celtic shipped three to Real Betis, two at Ferencvaros, and three in Leverkusen.

Yet they took full points form two meetings with the Hungarians, and held their own in a 4-3 thriller away to Real Betis, before being on the brink of a famous win in Germany.

Their lack of squad depth was exposed in the closing stages as Leverkusen roared back. Celtic's four substitutions came within a four-minute spell while they led 2-1, with all three forwards - Kyogo Furuhashi, Jota and James Forrest - departing along with defensive midfielder Nir Bitton.

Their replacements - James McCarthy, Mikey Johnston, Liel Abada and Albian Ajeti - had little impact as the hosts turned the tide.

McCarthy has yet to convince he can force his way into the team, while Ajeti is seemingly surplus to requirements and Johnston still finding his feet after long-term injury. Postecoglou requires more quality to call upon.

Former Celtic goalkeeper Pat Bonner says the team "didn't look as comfortable" after the substitutions.

"Kyogo instigated the press at times and they just looked a bit more insecure when he went off," said Bonner. "Bitton going off with a head injury is another critical player out of the team in that holding defensive role."

While Celtic's porous defence is a weakness, don't expect Postecoglou to suddenly change tact. The Australian espouses an attacking philosophy and is pleased with the way his team have gone at European opponents in his debut season.

Overall, Celtic's tally of 10 goals scored in the group phase is bettered by only five teams, including Leverkusen.

And Postecoglou's Celtic have proved adept at scoring via swift counter-attacks, with Jota's goal in Germany the latest example.

"In all our European games we've taken it to some very good opponents," Postecoglou said.

"We know there's a gap between us and the best but we'll bridge that if we keep taking this approach whenever we play these teams."

Former Scotland forward James McFadden says "the improvement" was clear in Celtic's performance.

"There was a real calmness about Celtic," he said. "When they were on the ball, they didn't go chasing it, they didn't go gung-ho.

"There were signs of improvement in their defensive shape, a lot of positives to take out of it. Get to January when they can bring in reinforcements, because they need that."

Europa Conference parachute

Although the visit of Real Betis to Glasgow next month is now a dead rubber, Celtic can console themselves with further European football in the new year.

Win their play-off against a Europa Conference runner-up next February and they are into the last 16.

While the Conference is the lesser of Uefa's three club competitions, it still boasts the likes of Roma, Feyenoord, Tottenham, FC Copenhagen and Union Berlin.

Celtic will potentially be bolstered by new arrivals in January, and the chance of going in deep European tournament is not to be sniffed at.