Dembele's season is over after undergoing a hamstring operation.
L'Equipe says on Tuesday night the president called the Frenchman, who had his hamstring operation in Finland, to reiterate that he counts on him.
Bartomeu told him he is part of the project for next season with Leo Messi and Antoine Griezmann in attack.
Dembele has barely been able to play half of the games since he signed for Barca for 105 million euros.
His contract expires in 2022.