Despite finishing on a high in May, Celtic spent much of last season dealing with turbulence on and off the pitch.
O’Neill was tempted out of retirement after Rodgers’ acrimonious exit, then returned for a second interim spell following Wilfried Nancy’s short stint as manager.
Supporters staged prolonged protests over what they saw as a lack of investment and the failure to reach the Champions League after losing to Kazakhstan’s Kairat Almaty.
That frustration carried into the summer after chief executive Michael Nicholson said the transfer market was proving “difficult”, citing competition with English Championship clubs and agent negotiations.
Asked about last season, McGregor acknowledged it was more demanding than recent campaigns.
He said overcoming such hurdles was essential and praised the players and staff who dragged the team through a tough year, noting that resilience is the foundation to build on.
He highlighted the need for strong characters willing to fight for one another.
Looking ahead, he hopes they can get back to their usual style and flair.
He added that the work done throughout pre-season is aimed at making that happen.
As McGregor suggested, Celtic will have a refreshed look in the weeks and months to come.
Influential Japan forward Daizen Maeda has departed for Premier League side Ipswich Town, while striker Kelechi Iheanacho rejected a new contract at Celtic and signed for Turkish club Bursaspor.
Goalkeeper Kasper Schmeichel has retired, and loanees Marcelo Saracchi, Julian Araujo, Tomas Cvancara and Benjamin Arthur have returned to their parent clubs.
On the incoming front, Camilo Duran and record signing Kasper Hogh—both with Champions League experience—have been added to strengthen O’Neill’s attack.