The deal has been done to bring the Argentine striker, nicknamed El Tanque, to the Stadio Azzurri d'Italia this summer.
"There's no maybe about it. We are just waiting for his agent Leo Rodriguez to arrive so we can put pen to paper with Denis," said Atalanta director Pierpaolo Marino.
"As for further reinforcements, we lack nothing in terms of creativity and quality. We will only make more changes based on the needs of the squad.
"The President doesn't hold back from making personal sacrifices for the good of Atalanta."