Millwall chairman John Berylson will refund the cost of match tickets for fans who watched their FA Cup third-round defeat at Bradford City.
The Lions lost 4-0 to the League One side, having had defender Mark Beevers sent off after five minutes.
The 456 supporters who purchased tickets in advance will be refunded.
American businessman Berylson thanked fans "for their continued support during difficult times" in a statement on the Championship club's website.
Millwall have won just one of their last 13 games in all competitions and are currently 22nd in the league table.
Manager Ian Holloway labelled their performance at Bradford as "unacceptable", described his team as "dysfunctional" and apologised to the club's fans in his post-match news conference.
Holloway has already made four signings since the transfer window re-opened earlier this month but Berylson has "pledged to facilitate further squad strengthening" in an attempt to improve results.