Blackburn have lost four games in a row and are 12th in the Championship, while Watford are up in third after winning three games on the spin.
Tony Mowbray praised his players for their performance in Saturday's 1-0 loss to Nottingham Forest, despite his side going a fourth game without a point.
Ultimately, though, Rovers are freefalling down the division and are surely out of the playoff picture, finding themselves 10 points adrift of the top six.
Not since April 2012 have Blackburn lost five straight league matches but, given the form of opponents Watford, that is a real possibility on Wednesday.
The Hornets have taken maximum points from their last three games thanks to wins over Bristol City, Preston North End and Derby County, scoring nine times and conceding twice.
However, Swansea City are only a point behind Watford and have two games in hand to play.
Watford beat Preston 1-0 last time out on their travels and are seeking consecutive away league wins for the first time since September 2017.
Not since 1981-82 have the Hornets completed a league double over Blackburn, meanwhile, which they will be looking to put right here to maintain their automatic promotion push.
Blackburn Rovers Championship form: WWLLLL
Watford Championship form: DLDWWW
Bradley Dack returned to the Blackburn bench against Forest and is in contention for a recall to the starting lineup here.
Mowbray will surely be tempted to make a change or two, with Barry Douglas another in the mix to return to the XI.
Armstrong fired a blank last time out, but the 24-year-old has 19 goals for the season and is behind only Brentford's Ivan Toney (24) in the division's top-scorers list.
As for Watford, captain Troy Deeney's prolonged absence has meant regular minutes for Pedro up top and that will remain the case at Ewood Park.
Francisco Sierralta was an unused substitute against Derby but could be part of Xisco's plans for this match.
Blackburn Rovers possible starting lineup:
Kaminski; Nyambe, Harwood-Bellis, Branthwaite, Douglas; Travis, Davenport; Elliott, Dack, Brereton; Armstrong
Watford possible starting lineup:
Bachmann; Femenia, Sierralta, Cathcart, Masina; Cleverley, Chalobah; Sarr, Hughes, Sema; Pedro
We say: Blackburn Rovers 0-2 Watford
Four defeats in a row have effectively ended Blackburn's campaign, with Mowbray's men neither in serious playoff contention nor at any risk of relegation.
Watford have a lot to play for and can potentially end the midweek set of fixtures in the automatic promotion zone with a fourth straight win, which we are backing them to pick up.