Bradford City have apologised after many fans encountered problems buying tickets for their FA Cup quarter-final with Reading.
Co-chairmen Julian Rhodes and Mark Lawn both said on Monday the League One club had been "naive" in their approach to selling tickets.
They had initially let season-ticket holders buy as many tickets as they wanted, at the club's discretion.
The club said in a statement: "We are sorry this situation has occurred."
However, City re-iterated that they were confident that all season-ticket holders would be able to purchase a ticket for the game.
Lawn said on Monday that any fan found to be attempting to sell on additional tickets purchased online at inflated prices would be banned by the club.
The club have now appealed for fans to contact them with any information on tickets being sold on via this method.
The game at Valley Parade on Saturday, 7 March kicks off at 12:45 GMT.