Gray who signed last night on an emergency loan deal, will be on the bench with Chris Dickson, who scored his first Addicks goal on Tuesday night in the FA Cup replay with West Brom.
Luke Varney will be alongside Chris Iwelumo upfront, with Izale McLeod missing out.
Jonathan Fortune is back from injury but will miss out on a starting place.
Possible team for Watford: Weaver, Moutaouakil, Bougherra, McCarthy, Youga, Ambrose, Holland(c), Zheng, Sam, Varney, Iwelumo
Subs: Randolph, Semedo, Thomas, Gray, Dickson