"Only in the comic book world do such processes (to improve) work that quickly and immediately," he told the Welt am Sonntag newspaper.
"But only in Melbourne will we know how far away from the competition we actually are."
Renault's Jean-Michel Jalinier has now admitted that Renault-powered cars will not be in a position to win in Melbourne, but he expects the picture to change significantly within "three to five races".
And Vettel said Red Bull is also working hard.
"The car we will use in Melbourne will only be the same as the one we tested in the winter on the outside," he said.
"Inside, it will be different," added Vettel.
"It's hard to say where we are, but we are certainly not among the favourites to win," he admitted.
New teammate Daniel Ricciardo, already in his native Australia, said the first challenge will be getting the RB10 to the chequered flag.
"We don't really know if it will last the distance," he told Fairfax Media, "because we haven't proven it (in testing)."