The new St Andrew's chief is hopeful winger Gray (ankle) will return after he trained on Monday.
Novak also missed Saturday's 0-0 draw at Wolves after suffering a hamstring injury on Friday and remains a doubt to face the Hornets.
Charlton loanee Michael Morrison stands-by to make his home debut and David Edgar is back from his one-game ban.
Winger Ikechi Anya returns to the Watford squad after missing Saturday's 3-1 win over Millwall with a dead leg.But defender Sebastien Bassong is doubtful after suffering a calf injury during the first half against the Lions.
With Gabriele Angella (ankle) and Gabriel Tamas (knee) still on the sidelines, Tommy Hoban is in line to start if Bassong is ruled out.
Midfielder Almen Abdi will miss out again with the shoulder injury he suffered against Nottingham Forest a fortnight ago
Source : PA