Watford will be without defender Marco Cassetti for the next two matches and centre back partner Gabriele Angella will also face a ban if he doesn't behave himself against Millwall.
Cassetti picked up his tenth booking of the season for tripping Michael Tonge during last night's 3-0 victory over Leeds United.
Ten cautions in a season results in an automatic ban if it is before the cut-off point, which is this Sunday.
Angella is currently on nine bookings so another caution at The Den on Saturday will mean a two-match suspension.
If a player receives 15 bookings in a season then he receives a further suspension and 20 would lead to a meeting with the Regulatory Commission.