Below-par showings were forgiven last season as Celtic simply just had to get by to stay in touch at the top before eventually leapfrogging Heart of Midlothian on the final day with a seventh successive league victory.
That Premiership-winning streak has been extended to 13 games following six straight victories to start the campaign, but concerns about performance level remain. Four of those six wins have been by a one-goal margin.
Twelve goals over three wins at Kilmarnock, Dundee United and in the first leg of the Champions League play-off against LASK sent an ominous warning to Celtic's domestic rivals amid a period of high spending, particularly in forward areas.
Camilo Duran has been the standout summer recruit so far with six goals and three assists in 10 appearances, while record signing Kasper Hogh and fellow big-money arrival Haissem Hassan are yet to fully settle.
Sutton said his old club have been "flat-track bullies" by "beating the teams you expect them to beat", but the collapse in Austria, plus Sunday's bruising loss, has highlighted glaring deficiencies.
Even captain Callum McGregor lamented Celtic's "team of individuals" after the weekend defeat at Ibrox.
Speaking on BBC Radio 5 Live's Monday Night Club, former striker Sutton also expressed his "great concerns" for O'Neill's men and said they have "big issues" after a "lightweight" midfield was "run all over" by Rangers.
Celtic have struggled to build up play against coherent pressing teams, which results in opposition sides being offered too much encouragement when the ball turns over.
They faced a whopping 60 shots across both legs with LASK. Forty of them came in a mess of a second leg. In the Premiership alone this season, they have faced 64 attempts, the same number as Hearts and six more than Rangers.
Over just six games, that tally already makes up almost a quarter of the total they faced in the entirety of the 2024-25 league-winning campaign under Brendan Rodgers.
That said, in comparison to last term, which was overseen by Rodgers, Nancy and O'Neill, Celtic's Premiership numbers show they are currently averaging a far better goal concession rate while scoring and shooting more.
Come Sunday, though, the most crucial statistic could be in the points column.
With a rapid rematch against Rangers offering the chance to move eight points clear of their city rivals after a test against European-level opposition, the next four days will at least be mood-shifting.
Whether that is to O'Neill's benefit remains unclear.
