McLaren sporting director Eric Boullier has revealed that he had genuine fears the team could have totally fallen apart last year as a result of its deteriorating relationship with engine providers Honda.
"My main worry at this time is not to have the team collapsing," he revealed. "I know the domino effect as well, you know.
"It takes years to build an F1 team but you can kill it in six months."
Boullier makes his comments in a new four-part behind-the-scenes documentary "Grand Prix Driver" made by Amazon.
It will be available for online streaming from February 9, but has been screened in advance for Autosport magazine.
Boullier explained that matters came to a head when the team's new car for 2017 performed much worse than expected in pre-season testing. It left McLaren's star driver fuming at the situation
"After this testing, Fernando is quite pissed off," Boullier says in the film.
"He is clearly saying I may reconsider my position to race because I'm not going to survive another year like this."
"He will not stay. I am a 100 per cent certain he will not stay..."
Boullier said he felt that if Alonso had walked out before the start of the season, the team wouldn't survive.
"In this business you know how it works," he say. "When you are weak, people they come, they just poach who they want."
The team's chief operating officer Jonathan Neale is shown briefing the team's engineers about the disappointing test in which he admits that Honda's performance had been a "shock" to the McLaren contingent.
"A line has been crossed," Neale tells them. "We are done. We've done that experiment about just trusting what is going to happen."
The documentary's producer Manish Pandey commended the team for allowing the filmmakers to get such a raw view of a team in crisis.
"It's no secret that this has been the most difficult season in McLaren's history," he said. "It would have been easy for them to close the doors on us."
He added that McLaren trusted fans "to recognise that all competitors take falls - but only great champions get up again, fight and win."