The 23-year-old smashed into the barriers with 18 seconds of the session remaining and faced an anxious wait to see if the damaged car can be repaired without incurring any grid penalties.
“With the crash, I don’t know where I’m starting tomorrow,” said Leclerc.
“I’m not feeling well for now, I’m just waiting for mechanics to open the gearbox.”
Red Bull’s title contender Max Verstappen was one of those who had to abort their final flying laps but the Dutch driver stands to inherit pole if the Ferrari needs a new gearbox, triggering a grid drop.
“It was all going really well and the red flag ruined the chance for pole,” said Verstappen.
Mercedes‘ world championship leader Lewis Hamilton, who leads Verstappen by 14 points after four races but had struggled through the session and in practice, qualified a distant seventh.
“We go back to the drawing board now,” said the seven times world champion. “There is a lack of grip, so that leaves you to overdrive the car and unfortunately it just didn’t improve.”
Leclerc had taken provisional pole after the opening flying laps, with a time 0.230 seconds quicker than Verstappen’s best, but got it all wrong at the Swimming Pool chicane.
“It’s a shame to finish in the wall, it doesn’t feel the same,” said Leclerc of what would be his eighth career pole and first in Monaco. He was last on pole in 2019.
Ferrari boss Mattia Binotto said it was too early to know whether the gearbox was damaged.
“We are worried but we are checking it,” he said.
The Monegasque has yet to finish his home race in two previous attempts, with last year’s race cancelled due to COVID-19.
Mercedes’ Valtteri Bottas qualified third, with Ferrari’s Carlos Sainz fourth.
McLaren’s Lando Norris was fifth and AlphaTauri’s Pierre Gasly starts sixth.