Gasly was trying to finish his fast lap towards the end of the session when he came across a gaggle of cars heading into the final corner, including Sainz, who was moving very slowly and was about to start his own lap.
Gasly had to abandon his lap and failed to progress out of the session in 17th place, while Sainz – who qualified eighth – later received a three-place grid penalty for impeding the Alpine driver.
The Montreal incident came after Gasly was himself penalised for impeding both Sainz and Max Verstappen in qualifying in Spain, although ultimately neither driver’s grid position was affected.
“I just think it's completely unacceptable to be driving the way Carlos did, it's just as simple as that,” said Gasly when asked about Sainz by Autosport. “Coming at 300, he’s sitting at 30kph in the last chicane just focusing on his own lap.
“But you're not alone on the racetrack. First of all, I could not even close the lap, which would have put us in a top six quite easily.
“And second of all, it was extremely dangerous, and it was just unnecessary. So I'm just absolutely gutted.”
He added: “I'm sitting here in P17 when we have the car and the pace to be in the top 10, eight or even top six in these conditions.
“I was in the opposite situation the other day, but the guys finished P1 and P2 and it didn't impact their Sunday.
“Now I'm sitting here in P17 and obviously, it ruined my qualifying and impacts my race a lot. So yeah, it's just not acceptable.”
Asked he thought there was a solution to the issue of drivers backing up he said: “I think we need to have a review because just seems to happen. Some guys got penalised in Monaco. Some guys got penalised in Barcelona, again this weekend.
“It wasn't such a problem in the past. So maybe it's something between drivers, between communication, I don't know, but clearly it needs to review because we're just moments away from having a much worse outcome because it's becoming dangerous.”
Gasly was adamant that he would have logged a quick lap had he not been forced to abort.
“It was my best lap, the track was improving so much,” he said. “The lap before I was doing a cooldown, so I can't remember but it was a second and a half or something like that. So looking at the data, I would have put us easily in P6.
“And even if they blocked me like two tenths, three times, it doesn't matter. At least I finish my lap and I can go through easily.
“You could not put your car in a worse possible place. And at the speed I'm coming as well he's just putting himself in a very dangerous position and also myself, it's just unnecessary.”
