The Lions are unbeaten in any competition since the middle of December and received another boost in mid-week with the news that a compulsory purchase order for the land surrounding their home stadium had been abandoned.
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Despite being a division below Watford in the league pecking order, Millwall will be confident of picking up a win after handily beating another Premier League club, Bournemouth, 3-0 in the last round of the FA Cup.
Watford made the final four of this competition last season and will be considered favourites to win this tie, but their form of late has been woeful.
They have won just two of their previous 10 games in all competitions, but a decent run in the cup could be just the catalyst they need to turn their season around.
Defender Shaun Hutchinson and striker Harry Smith are the only players unavailable for Millwall, while Watford could be tempted to give Mauro Zarate and M’Baye Niang a run after the pair signed from Fiorentina and on loan from AC Milan respectively.