As Red Bull and Mercedes fought at the front of the pack in both qualifying and the race, Ferrari failed to put up any kind of fight as it slumped to fifth and sixth place at the chequered flag.
Carlos Sainz led the Ferrari cars home in fifth, finishing almost a minute behind race winner Max Verstappen and nine seconds behind fourth-placed George Russell despite the Mercedes driver making an extra pit stop late on to get the fastest lap bonus point.
Leclerc was a further 10 seconds behind in sixth to end a difficult weekend for Ferrari, which spent the first half of the season closely battling with Red Bull at the front of the pack.
“It was incredibly difficult, we were just so slow, so yeah, we need to look into it,” said Leclerc after the race.
“We were in the middle of nowhere. With Carlos, we were way slower compared to the Mercedes and Red Bull, [but] much quicker than the midfield. So we were on our own, just a very lonely race.
“There wasn't much we could have done more to be honest today.”
The race saw Mercedes draw to within 40 points of Ferrari for second place in the constructors’ championship, leaving the Italian team looking over its shoulder heading into the final two races of the season.
But Leclerc doubted Ferrari would struggle as much in Brazil or Abu Dhabi as it did in Mexico, believing it had been an outlier within its season.
“I hope we won't be worse than this, because I don't expect any race worse than this,” said Leclerc.
“It's probably one of the worst races, together with Spa, this one. I honestly believe that it is a one-off.
“But for the future, we need to understand what we can do better in those conditions for us to be better.”
While Ferrari has been struggling with tyre degradation compared to Red Bull in recent races, the team found itself unable to run the power unit at maximum power due to the challenge of the altitude in Mexico City and subsequent concerns about its engine.
Ferrari F1 boss Mattia Binotto confirmed the team “didn't have the capacity to run maximum power” in Mexico, but felt there was more to explain its struggles as the car was “not comfortable with the track” all weekend.
“In terms of power unit, we were not at our best performance for the weekend, but I don't think that that's explaining the most,” he explained.
“That’s part of the equation, but there is more than that. There is certainly more than that, and it's something which we need to look at and there is not a clear answer right now.
“The ride was not great. The balance was not great. I'm pretty sure if I'm listening at the drivers later on in the debriefing, they will tell me that the car was not turning and the reason why I think it has to be looked at and we have not a clear explanation right now.”
Additional reporting by Filip Cleeren
