The Juventus director says the Chilean wing-back wants to stay in Turin despite interest from Inter, and has played down his side's chances of signing Juan Zuniga
The Chilean has endured a difficult start to life in Turin, making just a handful of appearances for the Bianconeri last term following his move from Udinese a year ago.
He has since been linked with a move to Inter this summer, but Marotta says he wants to stay at the club.
"Isla is our player,” the official told Sky Sport Italia. "I’m not denying Inter’s approach for him, but, with no substitute, he will remain ours.
"He’s told us that he would like to stay and, with boss Antonio Conte’s blessing, he is a Juventus player."
Marotta went on to say that Napoli defender Juan Zuniga, who has been liked with a move to Turin, will not be sold by his current employers this summer.
"We have a good relationship with Napoli and we accept that they will not be selling him," he added.
Finally, the 56-year-old said that his side are unlikely to make any more signings this summer, with their main priority offloading unwanted players.
"I don’t think we’ll sign anyone else. We’ve added to sections of the team that needed it such as the attack and defence," he added.
"We brought in a lot of players at the start of the summer, we have built a competitive team. In these tough economic times for Italian football, we have invested well.
"We have an attack that needs reducing because six players of that level are a lot. We want five, perhaps with a youngster to develop.
"The hope is that we find a positive solution for us. The requests will need analysing, but the desire of the player is more fundamental than that of the club."