Antonio Conte guided the Blues to a second league title in three years in his debut season as the Italian now seeks to improve his side with European football imminent next season.
While current Chelsea left-back Marcos Alonso only signed last summer a reported fee of £23m, Conte is looking to further strengthen in that position and had targeted £55m-rated Sandro, who joined the Champions League finalists from FC Porto in August 2015.
However, Marotta has confirmed that the London club's "very good offer" for the Brazilian has been rejected.
"Our desire is to not sell any of our most important players," Marotta said, as quoted on Sky Sports. "We said no to a very good offer from Chelsea for Alex Sandro."
"But we know that we are competing with clubs that are in a position to offer wages that are not rational for us. And players are always their own boss.I do not know how Alex Sandro reacted."
The news comes a fresh setback for Conte who was already making headlines for being reportedly frustrated at Chelsea's lack of investment in the transfer window so far, informing the club that he was open to leaving this summer.
According to Sky Sports HQ, however, Chelsea are confident that Conte will remain committed to the club and expect him to return for pre-season training in the first week of July.
It is also understood that technical director Michael Emenalo and director Marina Granovskaia are aware of Conte's transfer wish list and will continue with their recruitment efforts.