In a briefly red-flagged Q1 session, Leclerc reported a problem with his rear tyres over the radio as he struggled to hook up a solid qualifying lap.
After fumbling his first flyer, Leclerc was under pressure to secure a Q2 spot in the final seconds of the session, but he could do no better than 19th while team-mate Carlos Sainz sailed through in fourth.
Afterwards, Leclerc said he didn't know what was wrong with his Ferrari through Barcelona's left-hand corners during Q1.
"I don't have the answer. For now, the only thing I can say is that the left-hand corners were undriveable," he said.
"Through the right-hand corners the feeling was very similar to this morning, but 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 initially thought there was a problem with his tyres, but the issue persisted on his second set, which mystified him as he had no issues in Saturday morning's third free practice session.
"I thought it was the tyres on the first set, but then we went on the second set, and the feeling was exactly the same," he expanded.
"I just had no grip in the left-hand corners from the rears, so we'll check the car well and I would be very surprised if everything was fine.
"Even in the tricky conditions of this morning, I was feeling really good with the car, so there's something off."
As Sainz went on to take second on the grid behind Max Verstappen, in front of an ecstatic Spanish crowd, Leclerc revealed his car's odd behaviour nearly made him crash.
"I had so many moments and even during the first red flag I nearly lost it and put it into the gravel in a left-hand corner," he explained.
"This was just very, very weird behaviour, so we'll have to check the car."
