Vettel said that it would take until 2016 before Ferrari became serious challengers for the team and drivers title.
The German believes Mercedes aces Hamilton and Rosberg are "the ones to beat".
"It's 50-50 between them," Vettel told La Gazzetta dello Sport.
"Last year I didn't expect Rosberg to be so strong, especially in qualifying. Then in the races he was always really close to Hamilton.
"For me they will be the ones to beat."
When asked who would win in Melbourne on March 15, Vettel added: "There are two favourites, the Mercedes drivers Hamilton and Rosberg."
In the light of massive changes within Ferrari, the German has called for patience from fans expecting immediate success.
"It's difficult to say right now how strong we are. We need to be patient," he said. "But the car is definitely going well, both Kimi and I are happy.
"Ferrari is a team that has seen a lot of people come and go recently. We need time to adapt but sooner or later we'll get there.
"I don't know if it will be this year but if not then we'll be waiting for 2016," he added.