Celtic chief executive Michael Nicholson says the club's board "take responsibility" for their failing to reach the Champions League, while admitting they "did not achieve all of our objectives in the transfer window".
Writing in the club's annual accounts that go until the end of June and boast an increase in revenue, profit and money in the bank, chairman Peter Lawwell added that the Celtic board "recognise and share the frustration and disappointment of our supporters with respect to the timing of some of the incoming acquisitions".
It follows widespread criticism from fans regarding the club's transfer business this summer, as they failed to land a number of key targets before and after their Champions League exit.
Celtic lost to Kairat Almaty from Kazakhstan in the play-offs, but then went on to sign Michel-Ange Balikwisha, Marcelo Saracchi and Sebastian Tounekti before the transfer window shut, plus free agent Kelechi Iheanacho after Deadline Day.
While they did miss out on other targets, many supporters questioned why those who were signed did not arrive before the play-off tie - in order to help Celtic reach the league phase of the Champions League.
That followed manager Brendan Rodgers also publicly questioning the timing of signings, and insisting he would not stay at the club beyond this summer, when his deal ends, unless he was promised there would not be a repeat of the recent transfer window.
Many fans wrote an open letter to the club questioning their transfer plan and called for communication, while some also staged a late-entry protest directed towards the board while Celtic played Kilmarnock in the Scottish Premiership, entering the ground on 12 minutes to highlight their importance to the club.
Nicholson said the support of fans is "never taken for granted", while Lawwell added: "The board shares the ambition of our supporters to see the strongest possible team on the pitch and will continue to balance short-term performance with long-term financial stability, and we must factor in the long-term implications of all decisions made today. This strategy is vital to Celtic and has been pivotal to our success over the last 20 years."
The Celtic chairman also noted that after signing 11 players in the summer, Celtic spent £42.6m on transfers and agent fees during the year - more than double what was spent last year and marked "the highest single-season investment in the club's history, including twice breaking the club transfer record."
Lawwell added the "value of the squad is the highest it has been in the history of the club" with £77.5m spent over the last three years.
Following a season that saw Celtic win the Scottish Premiership, League Cup and reach the Champions League knockout play-off, the club posted a revenue figure of £143.6m - up 15 per cent.
While costs did rise too, £31.5m was recouped in player sales and a post-tax profit was up from £13.4m to £33.9m over the past year. Accounts also show the club have £77.3m in the bank, up by around £100,000 on last year.