Leclerc, last year's pole-sitter at the Circuit de Catalunya, qualified 19th but will go to the pitlane if, as seems inevitable, Ferrari need to work on his car to fix the problem.
The Monegasque suspected a mechanical problem rather than anything related to a new aerodynamic upgrade package introduced for Barcelona.
It was the first time since his home Monaco race in 2019, when Ferrari made a mistake with their timing, that he had failed to make it through the first phase of qualifying.
"I don't have the answer for now. The only thing I can say is that the left-hand corners were undriveable," Leclerc told Sky Sports television.
"The right-hand corners, the feeling was very similar to this morning. There's just something off in the left-hand corners that we need to analyse and understand because it was very far off what I expected."
Leclerc said he thought there was something wrong with his first set of tyres but the second set provided exactly the same feeling.
When told he was 19th he responded over the radio with one word - "unbelievable" -- but Leclerc later told reporters it came as no real surprise given the handling characteristics he was dealing with.
"I just had no grip at all in the left-hand corners from the rears. We'll check well the car and I'll be very surprised if everything was fine," he said.
"I had so many moments... these were just very, very weird behaviours.
"We'll have to check the car. Even this morning in the tricky conditions I was feeling really good with the car so there's something off."
