Sainz spent much of the Sprint battling with Fernando Alonso, but the thrilling fight ended in contact that saw Alonso retire with Sainz suffering damage that pushed him down the order.
Desperate to reclaim lost ground, Sainz lunged towards Leclerc as they approached the tight Turn 14 hairpin in the closing laps of the Sprint. The Spaniard appeared to lunge aggressively, forcing Leclerc off track and onto the run-off area.
Leclerc eventually held his nerve and secured fourth place while Sainz finished right behind, but the incident left a bitter taste in his mouth as the Monegasque said that Sainz was 'over the limit.'
The Ferrari duo replicated this result in Sunday's race, with Leclerc and Sainz finishing fourth and fifth respectively.
After five rounds, Leclerc holds a slender seven-point lead over his teammate in the driver's championship, but the China Sprint has cast a shadow over their internal dynamic.
Rosberg: Sainz 'over the limit'
Commenting on the battle between Leclerc and Sainz, F1 pundit and former world champion Nico Rosberg said, "First of all, it's great to see duels like this.
"That's fun as a spectator, but Carlos was over the limit. He didn't even try to catch the Apex. He was miles out and just drove Charles off the track.
"Charles was very angry internally too. I spoke to Charles' manager and Carlos apologized. Nevertheless, Fred talked to him again about being more careful, especially in the team.
"It's an important sign for Charles that the team boss also speaks the first word and it can't just continue like this, because otherwise, when you're in Charles' position and you see that nothing is being done, then it boils over and you become more and more aggressive. This is not good."