Manchester United were humbled at Watford last season - and Jose Mourinho is expecting an even tougher test at Vicarage Road this time around.
Late goals from Juan Zuniga and Troy Deeney gave the Hornets a 3-1 victory in September 2016, condemning the Red Devils to their third defeat in a week.
That period remains the lowest ebb of Mourinho's Old Trafford reign and the United boss is aware just how hard it will be to exact revenge on Tuesday evening.
Watford are eighth in the Premier League after their impressive 3-0 win at Newcastle, with manager Marco Silva's fine work leading to admiring glances from rudderless Everton.