Tommy Spurr has a dead leg, Richard Wood and Franny Jeffers are both struggling with groin injuries while Steve Watson has hurt his knee.
Wednesday, who take in two successive 1-0 league victories into the clash at Vicarage Road, will be at least happy to see September player-of-the-month Etienne Esajas back into contention.
The Dutch winger has missed Wednesday's last two games at home to Everton and Norwich but will hopefully return against The Hornets.
Wade Small is in good form and should retain his place while the likes of Kenny Lunt, Yoann Folly, Richard Hinds, Akpo Sodje and Lee Bullen will be hoping to win first-team recalls.