While the plot of Robinson Crusoe does not explicitly revolve around slavery, the institution of slavery serves as a basis for much of the action of the novel. When Crusoe heads to Africa, it is to purchase slaves. He himself becomes a slave and then soon becomes a slave owner. This idea of ownership and superiority impacts his relations with such people as Xury and Friday. Plus, Crusoe's wealth from his sugar plantations at the end of the novel would have come from slave labor.
The slave trade is the underlying force of most of Crusoe's profits.
Robinson Crusoe does not condemn slavery, but it doesn't celebrate slavery either.