Celtic have made a loss of £4m in the year ending June 30 after posting a profit of £11m in 2013-14.
The loss has been attributed to a drop in transfer revenue and failure in European competition last season, and the figures do not take into account Virgil van Dijk's £13m move to Southampton.
"Our decision not to transfer certain players' registration during the period, together with failure to progress in the UEFA Champions League, have had a significant impact on revenues and profits," chief executive Peter Lawwell told BBC Sport.
"Our core strategy remains focused on a football operation with a self-sustaining financial model and relies upon the youth academy, player development, player recruitment, management of the player pool, and sports science and performance analysis, to deliver long-term sustainable football success."
Celtic will compete in the Europa League this season, after losing to Malmo in the Champions League qualifying round.
