Another European outing ends in desperate disappointment for Scottish champions Celtic, with Martin O'Neill's men wilting again in Thursday's clash with Ferencvaros.

With the debacle away in LASK still very much in the memory, the Glasgow side had the chance to put things right in this Europa League opener, not least after Sunday's dismal defeat at Ibrox.

Alas, as has sadly become the norm in continental action, the men in green and white were taught a lesson by their Hungarian opponents, with two goals shipped in quick succession either side of the break proving decisive.

There were issues all over the pitch for the hosts at Parkhead in the 3-1 loss, but the first port of call has to be the defensive unit, including struggling centre-back Liam Scales.

Scales at the centre of Celtic defensive woes vs Ferencvaros

Scales, the great survivor at Celtic Park, certainly has his merits in the squad, with O'Neill quick to laud the Irishman in recent weeks, suggesting that he didn't know where the club would be without the 27-year-old.

The left-footer is a physical, dominant presence at his best, yet when off the boil, he really does look shaky and exposed, having so often been at the scene of the crime on Thursday evening.

Indeed, the away side's opener came courtesy of a Yusuf Bamidele strike that deflected in off the outstretched leg of the Celtic centre-back, while Scales also failed to prevent Kristoffer Zachariassen from flicking home just before the interval.

Now, the fault doesn't lie solely at his door, with Kieran Tierney undone defensively too for both of those efforts, yet those moments did epitomise what was a nervy showing in general from the man in the centre of defence.

Time and again, Scales drew the ire of the home crowd for his woes on the ball, so often dawdling in possession at a time when Celtic needed to try and ramp up the tempo.

In his defence, he did still walk away with a 94% pass accuracy rate, having lost the ball just seven times from his 113 touches, yet his struggles did spark a sense of unease among those ahead of him.

It seemingly wouldn't be a surprise to see Auston Trusty return this weekend in his place, with further selection decisions having perhaps also been sorted ahead of the weekend.

Why 3/10 Celtic star has played himself out of the derby

Not only was this a chance to start this year's Europa League adventure on a high, it was also an opportunity for O'Neill's men to stake their claim for a place in Sunday's starting lineup for the Premiership clash with Rangers.

The performance of James Forrest down the left flank was one key positive, yet there were far too many underwhelming displays elsewhere, among both starters and substitutes alike.

It proved a particularly difficult outing for the club's Danish duo, with Oliver Sorensen hooked at the break following another rather anonymous showing from the midfielder, while his replacement, Kasper Hogh, fared little better in the second-half.

That's not to say Camilo Duran was thriving in that centre-forward berth in the first-half, yet Hogh proved more of a hindrance than a help following his introduction, looking sloppy and sluggish again as Celtic failed to get back into the game.

Considering the £11m investment, O'Neill and co would be right to be expecting far more from their marquee striker, with the 25-year-old's hold-up play leaving plenty to be desired.

Time and again, the ball went astray when it needed to stick, with the former Bodo/Glimt star also resorting to committing fouls to ultimately kill any kind of momentum that the Hoops were starting to build.

It must be said that the service from the flanks was largely in short supply, with Sebastian Tounekti's lack of end product a continued concern, yet even so, Hogh did little to influence proceedings in a positive sense.

In all, he registered just 20 touches, losing the ball on ten occasions, having also won just two of his seven total duels while committing four fouls on the night.

Again, the lack of service may have been a factor, yet the Dane didn't register a single shot to boot, with only Benjamin Nygren really coming close to pulling a goal back for the beleaguered hosts.

Like with Scales, it wouldn't be a surprise to see Hogh slide back onto the bench this weekend, with there even a decision to be made over whether to unleash the lively Shim Mheuka instead, the teenager bizarrely omitted from O'Neill's Europa League squad.

Utilising Duran through the middle again from the off is also an option for the meeting with Derek McInnes' side, ensuring there's no reason to hand Hogh what would be an unmerited and undeserved start on Sunday.