Millwall are again without centre-back Shaun Hutchinson, who also missed last weekend's draw with Bradford because of a calf problem.
That means Reading loanee Jake Cooper - who made his Lions debut at Valley Parade - is again expected to deputise.
Mauro Zarate will be unavailable for Watford because of a suspension carried over from previous club Fiorentina.
Jose Holebas begins a two-match suspension following his 10th yellow card of the season.
WHAT THE MANAGERS SAY
Millwall manager Neil Harris: "It's an opportunity for my players to test themselves. This time we are playing one of the big Premier League boys on national TV.