A Mercedes engineer thinks it could take Ferrari "months" to alter the basic concept of its 2019 car.
Ferrari started the season with high hopes of finally breaking Mercedes' dominant grip on Formula 1 thanks to a fundamental change in the front wing rules.
But it is the Mercedes concept that has ultimately proved by far the best, winning the first eight races of the world championship.
However, Auto Motor und Sport said it has heard from Ferrari insiders that switching to a Mercedes-like front wing concept is actually a project only for 2020.
A Mercedes engineer is quoted as saying: "Before the season, we asked ourselves if Ferrari had chosen the better concept.
"But if we had changed the aerodynamics, it would have cost us four months," the engineer added.
It is believed Ferrari's actual response to its current situation is simply to change the setup direction at the races, favouring extra downforce in the corners over its current straight-line advantage.
"In the end we have to find more downforce," said Sebastian Vettel. "Then we can use the tyres better."
Until then, the German thinks runaway championship leader Lewis Hamilton is "playing" with Ferrari during the grands prix.
"I risked everything for the fastest lap," Vettel said after the French GP. "But Hamilton did the same laptime on worn and blistering tyres.
"Let's stop kidding ourselves -- Lewis is playing with us," he added.
Austria's Red Bull Ring could be a better layout for Ferrari, but Vettel warned that even that will not be enough to beat Mercedes.
"Maybe we should drive on the old Osterreichring, where there aren't many corners," the German joked.