The reigning world champion and favourite to retain his title this season uncharacteristically clattered into Aleix Espargaro at the Dutch MotoGP on Sunday, then crashed a second time.
Francesco Bagnaia won the race to move to 106 points in the standings (Quartararo still leads with 172).
“It was clearly a mistake from Fabio,” Guintoli said on BT Sport about the first crash. “He tried the lunge from too far behind.
“Everybody makes mistakes, even the best.
“He was wide, he had nowhere to go. He tried to make the bike turn but lost the front.
“So, we thought Fabio was indestructible and not vulnerable.
“But this is bike racing. You can make everything feel comfortable then, bang! Everything is out of order.
“He could have got injured in that crash which would have been a disaster.
“The season is still long. We have some tracks now where Pecco is strong - Misano, Aragon, then all the aways.
“If you have an injury, you are on the back foot.
“Going into the break for Fabio and Ducati, it is a boost.”
Quartararo was told to resume racing after his first crash then, after falling again, was visibly frustrated.
Michael Laverty told BT Sport why the Yamaha rider was sent back out to the track: “[To earn] one or two points on the board. They would have kicked themselves if he pulled into the garage but could have salvaged points.
“Fabio didn’t want to do it. The bike was damage, his tyres had cooled, maybe a sensor knocked off.
“The bike was rigid, the kickback threw him over the handlebars.
“It could have [broken] his collarbone.”
Fabio Quartararo: We spoke about being calm but I was the opposite
A brutally honest Quartararo reacted to BT Sport to his two crashes: “A rookie mistake. It was only the third lap and I acted like it was the last one!
“It was totally my mistake.
“I apologise to Aprilia and to Aleix for [putting] him out of the track.
“I thought there was a problem but the team told me to stop because the rain was supposed to come.
“It was normal to go and see him. He was the man of the race, amazing pace.
“It is normal to go and apologise in this situation.
“The only thing is the mistake in this race which was super-stupid. Of course I am happy but this race made me angry.
“I could have fought for victory but made a stupid mistake. I will learn from it.
“We spoke before the race about being calm but I was the opposite.”