Antonelli finished fourth for Mercedes but collected a five-second penalty and was demoted to sixth for repeatedly exceeding track limits.
"Kimi is so bad on wheel-to-wheel (racing). He moved under braking. It's unbelievable. We are going to crash," Leclerc, who finished third, exclaimed over the radio at one point.
Speaking later, the Monegasque toned down his comments.
"I was being a bit harsh maybe with the adrenaline inside the car," he said.
"It's true that we've had our moments with Kimi in the past and I hope this calms down a little bit going ahead. Especially as he's the only Italian on the grid against Ferrari.
"I wish it was with someone else. I really like Kimi as a person," added Leclerc. "It's just sometimes a little bit too close for comfort and not really needed as well. So in this particular case, I was quite angry in the car. But the comments were probably a bit too harsh."
Antonelli is the youngest championship leader in Formula One history and also the first Italian to win two races in a row since Alberto Ascari in 1953, an achievement that has ramped up expectations in Italy where Ferrari are also idolised.
The Italian made a poor start on Saturday, dropping from second to fourth, and struggled with low grip.
“After that, I was really frustrated and didn’t even drive well. I did a lot of mistakes and got track limits, which is something I need to avoid," he said.
“This weekend has been more difficult but it was expected with everyone bringing big upgrades. We just need to maximise the result and now focus on qualifying.”