Lillis will play as Joe Murphy serves a one-match suspension following his red card in the 4-1 loss to Blackpool two weeks ago.
Gary Hooper, the Iron’s top scorer, will be back having missed the defeat at Bloomfield Road with an illness. The left-back Marcus Williams returns from a leg injury.
Watford will include one familiar face for Scunthorpe fans, with Henri Lansbury impressing in their midfield on loan from the Premier League side Arsenal.
United know all about his ability as he was an integral part of the side that won promotion from League One via the play-offs.
Though he was ineligible to play in the semi-finals against Tranmere or final win over Millwall, Lansbury did play at Wembley wearing claret and blue as he was part of he side that lost the Johnstone’s Paint Trophy final to Luton Town.