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.
Source: Autosport