Charles Leclerc said he had no idea why Ferrari slumped so dramatically at the United States Grand Prix where he finished a distant fourth and team-mate Sebastian Vettel retired with a suspension failure.
The Italian team had reeled off six successive pole positions before their arrival at the Circuit of the Americas where Mercedes' Valtteri Bottas took pole and won the race, followed home by newly-crowned six-time world champion and team-mate Lewis Hamilton.
"I was not expecting that. It did not seem right. The first stint was extremely hard and I believe this was the main problem of the race, but to be completely honest I have no explanation," said Leclerc.
"The front left felt very weird. We need to analyse that because I've never had this feeling before. I'm pretty sure something was not right on this stint.
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"Then on the two others the pace was not as bad," he added.
Vettel said he had no explanation for his car's breakdown.
"I had a decent start, I was just on the dirty side - and then I had no place to go at Turn One. I was really struggling for grip, especially at right-handers. It was a very different car, so I asked if they had seen something or if something is broken," he added.
"A couple of laps after that we had the failure. I assume that it must have been an issue before. I don't know if it's related to the track, but on the other hand we've done so many laps. Why now, and not Friday?"