Dr Helmut Marko has said that Red Bull may not be in a position to push for the world championship in 2018.
Following the Mercedes versus Ferrari duel for last year's title, Red Bull tweaked their procedures so that they have a potentially winning car from the first race for 2018.
However, Marko told Auto Motor und Sport: "I don't think we're in a situation where we can go for the world championship."
The Austrian said that the 'power unit' era means Mercedes are clearly ahead, even if Renault should be stronger this year.
"The Renault engine should be more reliable and powerful in 2018, and we will fight with a competitive chassis," said Marko.
"But if Mercedes produces a new engine, the question is whether they will have an even bigger advantage. But we should be closer to them."
Marko said that if Red Bull do have an advantage over the top two teams, it is the driver lineup.
"When you have two equally strong drivers, both are looking for maximum performance and pushing the engineers to achieve the best possible result," he said.
"When you only have one driver who is going to the limit, you do not know exactly where you are."
Finally, Marko said that Red Bull's renowned car designer, Adrian Newey, is once again fully motivated for Formula 1.
"Adrian saw for the first time [since 2014] that we can beat Mercedes in a race where the engine behaves well.
"In the past we were stronger in the second half of the season, but the essential thing now is that we start strongly from the beginning."
Red Bull ended the 2017 constructors' championship in third place.
