The on-loan Barcelona striker will miss their clash with Las Palmas due to an ankle injury.
Pellegrini explained on Wednesday: "Vitor suffered a heavy blow to his ankle in the last game which limited him considerably in the second half. He was in even more pain yesterday and they are examining him to see what the injury is. In any case, he is not called up for tomorrow because he has not recovered.
"We will see what happens with Vitor Roque after the tests. I cannot give an opinion now because we do not know the severity or what type of sprain he has in his ankle."
Pellegrini also said: "We brought Vitor Roque knowing that he is 19 years old, a player in training who is lacking, not because of his age but because he has significant future potential. Perhaps he has missed many goals, if he had scored them the position in the table would be different, but perhaps Vitor Roque would not be here if he did not miss goals.
"He is a player in training who we hope has a great future and he is showing it with the dedication he has. They will go in for him, many other scorers go through moments when they cannot score and then they do. The opportunities must first be generated and he is generating them, then he has to have the success to convert them."