Watford have currently only sold 4,000 tickets for Tuesday's FA Cup third round replay with Bristol City.
Tickets for the tie are £15 for adults, £10 for concessions and £5 for Under-16s throughout Vicarage Road Stadium.
Season ticket holders had until 5.30pm yesterday to claim their own seats before release but then all seats were made unavailable until 10am this morning, when they were put on general sale.
Non-season ticket holders with a Fan ID number had also been able to buy prior to 5.30pm yesterday.
The winner of Tuesday's replay could face a trip to Manchester City in round four – depending on how the high-flying Premier League club fare against Blackburn Rovers in their own replay on Wednesday.