Captain Troy Deeney has already been ruled out with injury and the Hornets might lose two more of their star players.
"They are not training and we'll see in the next days if some of them can be available or not," said manager Javi Gracia. "In this moment they are doubtful.
"I'm sure we miss the players we don't have, but we don't complain about that.
"We have other players waiting and now is the moment to show the strength of our squad and try to show it in the next game.
"All the players are working well and I'm sure we are going to have a good performance."