Celtic say "profit from transfer of player registrations" was £14.1m, down from £21.5m, while "acquisition of player registrations" more than halved to £13.7m.
The club had cash reserves of £67.4m at 31 December, down around £10m from the figure posted for the year to June 2025.
Chairman Brian Wilson acknowledged there had been "a great deal of change and disruption" during the accounting period.
"Our exit from the Champions League in August 2025 was a bitter blow," he said.
"Appointing a manager in mid-season inevitably comes with challenges, and regrettably the implementation of Wilfried's style and ideas did not achieve our immediate objective of winning games and we took the difficult decision to part company with Wilfried in January 2026.
"We again turned to Martin, Shaun Maloney and Mark Fotheringham and their backroom colleagues to steer the club through to the coming summer and are pleased to have seen Celtic return to winning football matches in early 2026.
"We owe them and the players, who have also had to deal with change and uncertainty, a great debt of gratitude."
O'Neill recently described the prospect of meetings between the Celtic board and supporters' groups as "a big step forward" and hopes a "middle ground" can be found to end the acrimony around the club.
Some fans boycotted Saturday's Scottish Cup win against Dundee, the latest in a series of protests against the board's stewardship of the club and a perceived lack of investment in the men's first team.
And Wilson commented: "In recent months, the board has acknowledged that mistakes have been made. We are endeavouring to develop, enhance and refresh key areas of governance and strategies.
"The immediate priorities are to restore stability, achieve unity and deliver football success. These have provided the foundations for the achievements of the past 20 years – a period of outstanding success within the club's entire history."
Wilson also anticipated "a reduction in earnings" in the second half of the season, in keeping with previous years.

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