The Italian was picked up by the Scuderia to be their reserve driver for the 2017 season but had hoped to make the step up to drive for one of the Ferrari-powered teams in Formula 1 next year.
However, both Haas and now Sauber have turned down the chance give him a seat for 2018, Sauber opting to go with fellow Ferrari Academy driver Charles Leclerc to partner Marcus Ericsson.
Leclerc now appears to be ahead of Giovinazzi in the race to replace Kimi Raikkonen, who has a contract until the end of the 2018 season.
Marchionne is confident Giovinazzi will eventually become a full-time driver in Formula 1 though, claiming the 23-year-old just needs to be patient as he waits for a race seat.
"Giovinazzi is a good guy, and it's just a question time. He should get his chance," said Marchionne. "He will be Ferrari's third driver and he has a programme of testing with Sauber. We understand his desire to race, but at the moment there are no vacancies.
"The agreement with Sauber is a way to find an outlet for the youngsters in our Driver Academy, and it will take time to streamline this system."