Red Bull may not be able to challenge Mercedes until halfway through the 2017 season, according to the team's motorsport advisor Helmut Marko.
Mercedes's Winter Testing consistency and pace in the W08 has been impressive, though Red Bull's Daniel Ricciardo insisted the triple world champions can be beaten once competitive track action starts later this month.
Merc just ahead as records loom
But while Marko admits that Red Bull's engine suppliers Renault are making ground on their rivals, he is unsure whether they have made the necessary improvements to immediately topple the Silver Arrows.
"Of course Mercedes are still the favourite," Marko told Sky Sports News HQ. "They have the fastest engine and the most reliability.
"Renault is catching up, how much, we will see when we go to Melbourne. But we are positive that we can be very near to them. Mid-season, maybe."
Red Bull have been the third fastest team of Formula 1's new aerodynamic era so far, but are expected to launch their Australian GP-ready RB13 at Test Two next week.
It has instead been Ferrari who have taken the role of Mercedes' closest challengers, both in speed and reliability.
"Ferrari look strong, but you never know how much extra weight they have," Marko added. "It should be a fight between Mercedes, Ferrari and us."