Tasked with a rebuild of such scale, it is crucial Celtic do not repeat the mistakes of last season.
Incomings were left until the end of the summer window, by which time they were already out of Champions League qualifying.
Michel-Ange Balikwisha was brought in for a significant fee after weeks of talks and failed to have any impact.
Celtic were left with an imbalanced squad that lacked depth, particularly in forward areas, and supporters expressed anger at the board at both the lack of investment and urgency.
The Champions League play-off round – the stage at which they were beaten by Kairat Almaty – is looming large on 18/19 August this year.
It was not just in the summer where Celtic’s business flattered to deceive.
When O’Neill returned for his second interim spell after Wilfried Nancy’s sacking, he spoke frequently of the need to supplement his squad in the January window.
And yet none of the players signed on loan in January featured after the split. Some were injured, others evidently not rated or trusted by O’Neill.
That trend simply cannot continue this summer and Lambert believes O’Neill will play a big part in reshaping the squad.
“Hopefully he gets the players he wants to carry the club forward,” Lambert said.
“It’s a big summer for Celtic. I think what happened last year has given them a fright. What he did was galvanise things and I’m pretty sure he will have the last say on which players come in.”
Again, forward areas will likely be the priority, especially if Maeda does leave.
Celtic still have not effectively replaced Kyogo Furuhashi – who left two years ago – as their main striker, while Jota’s quality in wide areas is unable to be harnessed because of long-term injury.
Celtic’s attacking output has clearly regressed. In the 2024-25 title-winning campaign under Rodgers, they scored 112 league goals. Last term, they managed just 73.
Still, O’Neill can look back to the summer of 2000 – his first at Celtic – for inspiration.
Chris Sutton, Joos Valgaeren and Alan Thompson – three hugely successful figures for the club – were all signed under the Northern Irishman’s watch, before Neil Lennon followed in the January of 2001.
A summer window that replicated that one would go a long way to reshaping Celtic’s squad and easing any simmering unrest among the club’s fanbase.
