The Montenegro international had been connected with a move to Serie A rivals Juventus, who were believed to have offered the Viola €13m plus a couple of players for the 23-year-old in January.
However Jovetic, who has notched up nine goals in 18 Serie A matches this term, is going nowhere according to Cognigni, who is determined to keep hold of the club's star players.
He told La Gazzetta dello Sport: "It's not possible that there will be any negotiations with Juventus for Stevan.
"In fact, it's not possible to deal with them or anyone else: Jovetic is not for sale.
"He is happy at Fiorentina and has a contract with us for another three years."