Charlton plc chairman Derek Chappell has announced the club made a net loss of £11.5m loss during the last financial year, ending June 2008.
Finances at The Valley have suffered due to the team's failure to win promotion back to the Premier League.
The Addicks are currently bottom of the Championship, five points from safety.
In the club's annual report Chappell said: "Our football performances have simply not been at an acceptable level and this must change."
Chappell, who took over as chairman in March, added: "Our main task now is to secure our place in the Championship through improved performances and success on the playing field during the remainder of this season.
"Everyone connected with the football club remains determined to achieve this. We require full support for the team and its management and a united approach both on and off the pitch.
"Football clubs revolve around success on the pitch and ultimately this is essential for the continuing development of this football club."
Charlton were relegated from the Premier League in 2007 and missed out on a place in the Championship play-offs last season.
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