Uncertainty over the future of McLaren's relationship with Honda ultimately led to Sauber pulling out of its own engine deal with the Japanese manufacturer as it couldn't guarantee a gearbox supply for 2018.
Sauber announced its plans to use Honda engines next season at this year's Russian Grand Prix, but by the end of July the deal was annulled. At the time, newly-appointed Sauber team principal Frederic Vasseur said the decision had been for "strategic reasons" but in an interview with Formula One's official website this week, he confirmed the absence of a firm gearbox supply was the main sticking point.
"Leaving aside the current issues that Honda has with reliability or performance, as I know that they will come back at some point, the biggest concern for us was that we could not secure the responsibility of the gearbox," Vasseur said. "We don't have the resources internally to build our own gearbox, so we knew that we had to deal with someone.
"With Honda we would have to deal with McLaren, but I was not so confident that McLaren would continue with Honda. So it would have created a strange situation: asking McLaren to provide the gearbox for a Honda engine when McLaren could be running another engine. With this kind of scenario I was absolutely not confident. So the 'reprocessing' of the Honda deal was one of the biggest issues for Sauber."
Sauber replaced the Honda deal with a supply of up-to-date Ferrari engines for 2018 and Vasseur said a decision needed to be made quickly in order to make solid progress on next year's car.
"Sauber had already started the design of the 2018 car before I took the decision and that was the reason for the rush -- so as not to throw good money at abandoned projects. The design was already in progress, then there was the factory shutdown, so we had to take the decision right away."
Honda's future in F1 remains in doubt with McLaren yet to make a firm commitment to the Japanese manufacturer for 2018.