Sebastian Vettel has admitted there was "something wrong" with his original 2014 chassis.
After Barcelona, where the German impressed at the wheel of Red Bull's winter testing monocoque, it was reported that the team had discovered a 'bend' in the car with which Vettel struggled during the first four races of 2014.
Red Bull immediately denied the report.
But the story has now been repeated by the major German daily Bild-Zeitung.
Vettel is quoted as saying: "I knew there was something wrong. I had lost all trust under braking for the corners and accelerating out of them."
Dr Helmut Marko, Red Bull's outspoken director, does not deny Vettel's claim that something was "not right" with the car Vettel originally dubbed 'Suzie'.
"The chassis was not really bent, but in some places it just was not one hundred per cent right."
Marko said Vettel will stay at the wheel of the winter testing chassis for the time being, "but soon he will get a new one".
Reigning quadruple world champion Vettel is not even ruling out his first win of the season next weekend in Monaco.
"At Monaco you don't need as much engine power as you do at other circuits," he is quoted by SID news agency.
"Maybe some rain could help us as well. There is always a chance to win," added Vettel.