Max Verstappen fears that Red Bull is still going to face a "painful" time on the straights, with the team's engine supplier Renault having yet to close the gap on Mercedes.
Although Red Bull appears to have made good gains with its chassis and has emerged as the outfit many are tipping to be Mercedes' main challenger for wins, Verstappen is more cautious about the team's potential.
In particular, he thinks that the team could still be left on the back foot if it is too far down on power against its main opposition.
"I think the car compared to last year definitely made good improvements again," said Verstappen ahead of the Australian Grand Prix.
"For sure everybody improved, but from my personal feeling I think we have quite a strong car. But we have to wait and see how good our overall package is with the straights here.
"It is definitely going to be a bit painful there. But for sure I am optimistic, but also realistic. We have to wait and see."
Asked if he felt that Renault had made as much progress with the engine as Red Bull had with the car, he replied: "Um...not as much!"
Although Red Bull is pinning hopes on Renault making progress with its power unit over the course of 2018, Verstappen thinks it is important his team pushes hard with its car as well.
Pushed on whether the engine was the only thing stopping Red Bull fighting for the championship, he said: "And the development of the car. We have to be on top of that as well compared to Mercedes and Ferrari.
"I think in the past it has always been a strong point of Red Bull, the development during the season. We have to wait and see how it is going to be this year again, it is a different year again.
"I'm confident in the team that they can build a great car and maintain that. But like I said before, it is more about the overall package that needs to be right."
Additional reporting by Erwin Jaeggi