Red Bull team advisor Dr Helmut Marko says that its former engine supplier Renault is partly to blame for Red Bull's aerodynamic issues in 2019.
The energy drink squad has suffered from aero problems at the opening four races of the season, but insists that it will be introducing a fix at this weekend's Spanish Grand Prix.
Red Bull split from Renault at the end of the 2018 season in favour of Honda, who spent 2018 with Toro Rosso. So far this year, Red Bull has picked up one podium finish, which came at the season-opening Australian Grand Prix.
Marko praised the Japanese manufacturer, saying to Auto Bild that "until now, the lack of downforce has been our problem".
"The design of the car was due to the lack of engine performance of our former engine partner, so we had to design for efficiency", Marko added.
"We have lost time in the corners, but Honda has significantly improved their performance and we can now react."
Marko believes that Max Verstappen has been the only consistent driver so far this year.
After picking up a podium in Melbourne, the Dutchman followed it up with a series of fourth place finishes, splitting the Ferraris at the finish line in Bahrain, China and Azerbaijan.
Marko is confident that Verstappen is ready to fight for a world championship now that he is in his fifth year in Formula 1.
"Hamilton, Bottas, Vettel and Leclerc have all had their ups and downs," Marko commented.
"Only Max has been flawless so far and has always made the most of the car. Max has even done more than the real potential of the car.
"He is completely ready for the title. In Barcelona we now have to prove that we are too."