Both Leclerc and teammate Carlos Sainz felt a lack of power on the high-altitude circuit, and some competitors suspected that the team may have somehow tuned their powertrains in search of reliability.
Sainz suffered a severe engine failure earlier this year at the Red Bull Ring, another venue where altitude is an issue, and a non-finish in Mexico could cost the team dearly in the race for second place in the championship.
Leclerc suffered more than his team-mate on Saturday and also had a DRS problem on the back straight during the final run of Q3, leaving him only seventh on the grid. Telemetry showed the pit that the DRS had worked correctly, but the flight engineers could see that the Leclerc was still fully loaded.
Leclerc’s weekend was already compromised by a heavy crash in FP2 that damaged his gearbox.
“There was something weird or wrong with the engine,” he said when asked by Motorsport.com about his qualifying session. “I lost quite a lot of time on the straights from FP3 to Q3, not compared to Red Bull or Mercedes because it’s been that way since day one and we knew it.
“But, yes, there was something strange. Also, the engine didn’t really respond to the throttle I did at high speed.
“So I really hope we can resolve these issues on Sunday. Otherwise, it will be an extremely difficult race to be consistent.”
Carlos Sainz, Ferrari F1-75
Photo: Andy Hone / Images of motor sports
Both Ferraris looked difficult in the high-speed corners, but Leclerc admitted he found it difficult to judge: “Honestly, it’s very difficult for me to comment on the balance because there was really a lot of inconsistency at high speeds and it wasn’t going to do exactly what I wanted with an engine.
“So I’ll be surprised and then I’ll get the snap. So yeah, it’s hard to compare the balance because it was pretty good when the engine responded to what I was doing. But it was very inconsistent.”
He added: “It was quite difficult on the kerbs. Unfortunately, very strange things happened on the bumps as well.”
Sainz noted that he felt that was unusual Ferrari will be stronger in Sunday’s race than in qualifying. However, Leclerc was not so optimistic.
“Again, unfortunately, I cannot comment from my end. If I have the same problems, the race will be a nightmare. So I hope we can fix it.”
Leclerc insisted that his engine problem was not only due to the altitude of the track: “It’s been happening since the start of FP1, with the altitude obviously you lose performance.
“Both Red Bull and Mercedes seem to be stronger than they have been all weekend. But for me there was something more specific in FP3 and qualifying and I still don’t know what the problem was.”