Martinez scored a first-half double in Inter's 2-1 win over SPAL on Sunday to fire his side to the top of Serie A and take his goals tally for the season to 13 in all competitions.
The 22-year-old's impressive start to his second campaign in San Siro has seen him emerge as a rumoured target for LaLiga champions Barcelona in recent weeks, as they look to identify a long-term heir for the aging Luis Suarez.
Despite Martinez's agent talking up a potential switch to Barca in the past, Marotta is not concerned by the rumours surrounding the Argentina international.
"His contract situation is not compromising," Marotta said at Monday's Serie A assembly. "He is a good boy and is grateful to Inter, so it does not cause a discomfort.
"Inter and Suning [the club's ownership group] aim to grow and you can't do that by giving up your best players. But the market is unpredictable - there is always the will of the player to choose their own destiny.
"This is not the time to talk about a possible transfer or contract renewal. Lautaro knows very well the trust we have for him."
Eight of Martinez's goals this term have come in Serie A, while strike partner Romelu Lukaku has scored 10 times in the Italian top flight since arriving from Manchester United.
Marotta has hailed the duo's chemistry in attack, with Inter not previously boasting two players with eight or more goals at this stage of the campaign since 2001-02.
"There is the right chemistry between them," he said. "Antonio Conte, a proven winner, knows how to get the best out of them.
"They are friends off the field and have a great harmony on the pitch."
Inter spent big during the close season to bolster their squad, but Marotta has not ruled out further incoming activity when the transfer window reopens next month.
"We will evaluate the squad because we need to plan for certain situations, and we are lacking in certain areas," he said.
"At the same time we have to bear in mind what this group has achieved with the guidance of Conte. We look at the window with optimism, but also with realism."