PSG signed the Brazilian international for a world record £50m last week, but Blanc has dismissed suggestions that his compatriot will make way.
He told RMC: "[Marquinhos] is staying, it is sure and certain. What interests me is to keep the same number. Certainly there will be departures.
"Dani Alves is one of the top players at his position. There is already David Luiz, who is a very good recruit. We will certainly take one or two more players."
Marquinhos signed from Roma for around £30m last summer.