Manchester United have made two bids for Fabregas already as they look to make a statement signing under new manager David Moyes. Both offers have been turned down by the Spanish champions.
“Evidently I’m not going to talk about the financial interests of the club," Martino said, "but if the club have turned down United’s offers two times in this case I add a third rejection.
“So we are going to keep him here.”
Martino spoke as he was being unveiled as Barcelona manager - Fabregas' future is believed to be high on his agenda as he steps into the role.
The 26-year-old returned home to his boyhood club in 2011 after several stand-out years at Arsenal.
Barcelona vice-president Josep Maria Bartomeu added: “Whatever offer United make, however big, we will say no. Cesc Fabregas will stay a Barcelona player.
“That United shows interest in Cesc Fabregas is normal. He is a truly great player. It doesn’t annoy us.
"It gives us pride to have such a good player in our team that United want him because they are a great club.
“But whatever offer arrives from them we are not going to sell Cesc Fabregas. We are counting on him."