Romain Grosjean says he endured "one of the worst races of my career" in Barcelona on Sunday.
Finishing two laps down and dead last was a far cry from the Frenchman's pace on Friday, when he was fifth and sixth fastest in the two practice sessions.
But L'Equipe quoted the Haas driver as saying after the race: "It was hell. Honestly, the car was undriveable. One of the worst races of my career.
"It was horrible - the car was nowhere from the first time I turned the wheel. I don't know what happened between Friday and Sunday but it wasn't the same Formula 1 for me," Grosjean added.
"It may have been the worst car I have driven in my life."
Haas boss Gunther Steiner responded: "I will not comment on the words spoken every day about best car, worst car.
"What matters is to take a step back and analyse why we went from strong on Friday to struggling on Sunday. We lost two seconds per lap which is very strange."
As for whether he appreciates Grosjean's forthright comments, Steiner added: "I am used to these sorts of strong words from my drivers.
"It is true that some words do not help us, but I will survive," he added.
