Max Verstappen says a mechanical set-up error was to blame for Red Bull's disappointing performance in Formula 1's Bahrain Grand Prix.
The Dutchman, who said the issue came to light during the two-day test after the race weekend, added the wind had also played a factor.
Verstappen qualified fifth, only sixth thousandths ahead of Haas's Kevin Magnussen, while team-mate Pierre Gasly started 13th before advancing to eighth.
"We understood already a lot in testing, and we also found out we made a mistake with the set-up, the whole week, unfortunately," he said.
"That's how it goes. As long as we found it [it's OK]."
Asked to elaborate, he said the error was "big enough" and "mechanical," and that it affected both his and Gasly's cars.
Verstappen said Red Bull would have been closer to the leading Ferraris and Mercedes cars had everything been perfect.
"If we could find a good balance within the car I think we could definitely be fighting closer, yeah," he said.
"Then for sure, we would have finished third [ahead of Charles Leclerc's ailing Ferrari] in Bahrain.
"It was windy throughout the whole weekend.
"I was never happy with the balance, always trying to get it, but we never got it.
"With what we found we could understand why we couldn't find a good balance.
"If there's something set up wrong, like we had, then you can do whatever you like on the car, and you will always have the same issue."
Verstappen said the error was not specifically to blame for the team's struggles on the softer tyres in Bahrain, and added the set-up issue would be "a simple fix" for the Chinese Grand Prix.
Red Bull boss Christian Horner said after the Bahrain race that Red Bull felt its chassis was in greater need of sorting than its Honda engine.
But asked by Autosport if the RB15 was the most difficult F1 car to set-up that he has experienced, Verstappen compared it favourably to its predecessor.
"To be honest not," he said. "I feel comfortable in the car, and I drive it as fast as I can.
"But for example in Australia we did quite a good job to be fourth [in qualifying], even in Bahrain to be fifth I was actually quite happy.
"At the moment it's just not really quick enough. But like I said before, in Bahrain we found some issues.
"I feel comfortable, there's nothing wrong with that. I feel better in this car than last year's car."