The on-loan Manchester United midfielder, who has hit 10 goals this season, has missed the last two games with a knee injury but has been passed fit.
Boss Malky Mackay can also call upon on-loan striker Heidar Helguson, who would have been ineligible to face parent club QPR on Tuesday night but the game was postponed.
Winger Will Buckley, the January signing from Rochdale, will have to wait a little longer to make his debut as he is still struggling with a thigh strain.
Mackay has an otherwise fully-fit squad to choose from as the Hornets go in search of their first away win since October.
