Sebastian Vettel, championship leader Lewis Hamilton's main title rival, is 59 points adrift of the Mercedes driver after retiring from Sunday's Japanese Grand Prix with a broken spark plug.
Ferrari are also a hefty 145 points behind reigning champions Mercedes in the constructors' standings with four races remaining. Both titles could be wrapped up in Austin, Texas, in two weeks' time.
Japan followed two other bad races for Ferrari, with Vettel starting last in Malaysia after being sidelined in qualifying by an engine problem. He crashed out in Singapore on the first lap after a collision with team mate Kimi Raikkonen.
"The season is not lost, there's still all to do," Marchionne told Italy's Class CNBC television at a Ferrari 70th anniversary event in New York.
"I won't talk of bad luck, I don't believe in it," he added. "The important thing is to not lose the confidence that has brought us so far.
"I'm delighted with what the team has done and I have tremendous confidence that in the next four races we will be able to close most of the Mercedes gap."
Marchionne expressed annoyance that a 59 euro ($69) part, in a car costing millions, had wrecked the race and repeated a view expressed after Malaysia that component quality and procedures needed to improve.
"It's a problem we've probably ignored over time because it was never of much importance but now we've had at least three occasions where we've really seen the devastating impact on performance. We'll fix it," he said.
Raikkonen was unable to start in Malaysia, having qualified on the front row, after a power unit problem was detected just before the race.
Marchionne said Ferrari, who failed to win any races last year, had still made huge steps with Vettel winning four times this season and leading the championship from March to September.
"Without being arrogant, I think it (the car) is at the same level if not better than Mercedes' today," he said. "I'm sure if we'd not had any problems like in the last three races, we would be having a different discussion."
(Reporting by Alan Baldwin, editing by Ken Ferris)
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