Scunthorpe will have Cliff Byrne available for the visit of the Hornets.
The Iron skipper was booked in the 3-0 defeat at Doncaster on Saturday, his fifth of the season.
But the defender will not face a suspension for the Hornets clash because FA rules state players picking up five cautions after December 31 will only receive a warning.
That reprieve could hand boss Ian Baraclough a massive boost as they look to pull out of the bottom three.
However, Michael Raynes (thigh), Niall Canavan (knee) and Jim McNulty (ankle) are all set to miss out.
United may tinker in the search of some much needed penetration and Baraclough is keen for a reponse, saying: "People seemed to go into their shells a little bit and that's something we need to improve."
Watford boss Malky Mackay is waiting on the fitness of captain John Eustace.
The veteran midfielder has only missed two games in all competitions this season but is struggling to make the Iron clash after picking up a calf strain which forced him off after an hour of the 3-0 home win over Portsmouth.
If Eustace is passed fit Mackay is likely to name the same starting XI for the third match running.
Midfielder Stephen McGinn remains sidelined with the broken cheekbone and eye socket he sustained against QPR earlier this month and will be out for at least another four weeks.
Teenage midfielder Piero Mingoia is fit again after a thigh injury and could be among the substitutes but the game may come too soon for winger Michael Bryan as he continues his recovery from a niggling ankle injury.