Jenson Button said his McLaren was "scary" to drive and does not expect to score a point in 2015.
The 2009 world champion finished 16th at the Spanish Grand Prix, ahead only of the back-of-the-grid Manor cars.
"The first 30 laps were the scariest of my life," Button said.
"Every time I touched the throttle at any speed, the rear was just gone. It wasn't normal. In low-speed corners it was just slow, but high speed, very scary."
McLaren had come to the Spanish GP hoping for their first points of a season that has started uncompetitively as they embark on a new engine partnership with Honda, whose power-unit is more than 100bhp short of the best.
But Button said after the race: "After today I don't expect points at all this year, but hopefully today was an off-day.
"It did not feel right. The weekend has been reasonably good for us, I have been happy with the way the car's been but in the race it was like flicking a switch."
Button's team-mate Fernando Alonso did not have the same handling problems with his car, but retired with brakes failure after 26 laps.
Alonso could not stop in time as he came in to retire, and his car knocked the mechanic who was operating the front jack into the air. The man was unhurt.
"Scary but everything was fine," Alonso said.
The Spaniard had run as high as seventh in the race as the pit stops unfolded and was 14th when he retired. He said he felt finishing ninth or 10th had been "possible".
He added: "The progress is coming. We are a long way off so we need to make double steps because everyone else is improving during the season.
"This is a very challenging project, but we are recovering well and we need to keep it up."