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.