A single week in mid-September may well define Celtic's entire season. After a sobering 3-0 defeat to Rangers in the Premier Sports Cup quarter-final at Ibrox, manager Martin O'Neill's side face two rapid-fire tests: a UEFA Europa League opener against Ferencvaros on Thursday, followed by a league rematch with Rangers on Sunday.

Anxiety in the stands

Celtic supporters are already on edge heading into European competition, their nerves still raw from the Champions League play-off collapse in Linz. That capitulation, combined with Sunday's derby thrashing, has prompted genuine questions about this squad's ability to deliver in high-stakes matches.

O'Neill, however, showed little patience for outside criticism when questioned about his team selection. "It's strange you're never asked about team selection when you win games," he said. "We've been doing a fair amount of winning domestically now for quite some considerable time and we've won our league games so far. It's another big test for us on Sunday, obviously, but it's amazing the number of times you're not questioned when you've won."

Structural concerns beneath the surface

Celtic's Scottish Premiership form looks strong on paper — six straight victories, extending their title-winning streak to 13 league games. Yet four of those six wins came by a single goal, and the manner of performances has left sections of the support unconvinced.

Former Celtic striker Chris Sutton used his platform on BBC Radio 5 Live's Monday Night Club to air serious misgivings. He described his old club as "flat-track bullies" who have been "beating the teams you expect them to beat", and expressed "great concerns" about the squad, stating they have "big issues" after a "lightweight" midfield was "run all over" by Rangers. Even captain Callum McGregor conceded Celtic had been a "team of individuals" in the Ibrox defeat.

The data adds weight to those concerns. Celtic have faced 64 shots in the Premiership alone across just six matches — the same number as Hearts over the same period, and six more than Rangers. Against LASK in the Champions League play-off, they conceded a staggering 60 shots across both legs, 40 of which came in a chaotic second leg in Austria.

Bright spots in attack

Not everything points downward. Summer signing Camilo Duran has been a revelation, contributing six goals and three assists in 10 appearances. Record signing Kasper Hogh and fellow big-money arrival Haissem Hassan are still finding their feet, but the attacking investment is evident.

It is worth noting that, compared to last season's turbulent campaign — which cycled through Brendan Rodgers, Wilfried Nancy, and O'Neill — Celtic are currently conceding at a better rate while also scoring and creating more chances in the Premiership.

Four days to shift the mood

O'Neill was brought in last January to stabilise a chaotic campaign and ultimately delivered a Scottish Premiership title and Scottish Cup double. Supporters were divided over whether to let him depart on that high or continue — but they were united in demanding European progress and more attractive football. Neither wish has been granted yet.

A positive result against Ferencvaros on Thursday, followed by a derby victory on Sunday, could move Celtic eight points clear of Rangers in the league and dramatically alter the narrative. Whether O'Neill can engineer that turnaround is the defining question of his second season in charge.