Lloyd Doyley (hamstring), Essaid Belkalem (ankle), Ikechi Anya (calf) and Tommie Hoban (ankle) are all definitely ruled out of the encounter.
Goalkeeper Manuel Almunia (illness) and defender Gabriele Angella (thigh) are doubts, while Troy Deeney (dead leg) and Sean Murray (back) have returned to training this week and will be assessed along with long-term absentee Almen Abdi (foot).
The Hornets are boosted by the availability of Lewis McGugan after a one-match suspension while recent addition Fitz Hall has been given the green light having not been cleared in time for last weekend's defeat to Bolton.
Yeovil's trio of loan signings, meanwhile, look set to be involved.
Manager Gary Johnson was busy on deadline day, adding Liverpool striker Adam Morgan, Nottingham Forest forward Ishmael Miller and Everton midfielder John Lundstram to his squad, and all three could make their debuts at Vicarage Road.
But Johnson will be without captain Jamie McAllister for a fortnight after he picked up a shoulder injury in their 2-1 loss to Doncaster last Friday.
Liam Davis replaced him at The Keepmoat and the former Coventry man looks set to get the nod from the start while McAllister is sidelined.