The Hornets have so far sold more than 2,500 tickets for Saturday's trip to Manchester City's Etihad Stadium.
Watford took 6,000 supporters to City's ground when the teams met in the FA Cup last season but the Golden Boys always looked unlikely to match that feat for this year's fourth round tie.
At present, Watford's season ticket holders and those who have purchased tickets during the 2013/14 campaign can buy tickets for Saturday's match.
Watford say 'general sale' will start at 9am tomorrow but fans need an eligible Fan ID. A Fan ID can be obtained online at watfordfctickets.co.uk.
Tickets are £15 for adults, £10 for concessions (over-65s and 16-21 year olds) and £5 for under-16s.