Marotta was speaking at the unveiling of Juve's second reinforcement to the forward line as Fernando Llorente finalised his move from Athletic Bilbao to join Argentina international Carlos Tevez in Turin.
The Bianconeri are eager to further bolster their ranks ahead of a second defence of the Italian title - and a tilt at the Champions League - but Marotta revealed hostility from Fiorentina could prevent Montenegro forward Jovetic from moving north.
He told juventus.com: "A lot has been said about Jovetic but difficulties in our relationship has made any deal difficult.
"At the moment I don't think it will be possible, but a lot could happen between now and the beginning of September."
He was, however, more optimistic above Juve's prospects of snaring Italy defender Angelo Ogbonna from city rivals Torino.
"Ogbonna is a target, we've never disguised that fact," he added. "We have a great desire to bring him here and we're in talks with (Torino president Urbano) Cairo, we'll see what happens at the end.
"The coach's preference, and ours, is to have the squad decided before the summer training camp starts, but we know the transfer market is difficult and that bartering has become more and more important.
"Juventus start with the assumption that the squad has been competitive enough to win two league titles in a row. And with Llorente and Tevez we have reinforced further."