McLaren is currently deciding whether to commit to Honda for another year or switch to another supplier, with Renault its only realistic alternative.

Sauber and Honda agreed to call off their deal for the latter to supply the Swiss team with engines in 2018, with Sauber choosing to continue with Ferrari power for next season.

McLaren had been set to supply Sauber with a gearbox as part of the Honda deal, but Vasseur said he questioned that arrangement given the uncertainty of the McLaren-Honda’s relationship.

“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 told the official F1 website.

“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.”

Sorting out the engine situation was one of Vasseur’s first tasks when he took over from Monisha Kaltenborn as team principal, with the former Renault chief keen to limit the impact a delay would have on the shaping of the 2018 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,” he said.

“The design was already in progress, then there was the factory shutdown, so we had to take the decision right away.”

Sauber is currently 10th in the constructors' championship and Vasseur conceded it will be challenging to lift the team above McLaren into ninth before the end of the season.

"I am very honest: it would be very difficult to jump to P9," he said.

"McLaren is in P9 today and McLaren is two times Sauber in terms of manpower – maybe even a bit more – so they have the capacity to improve faster than us. And they are already faster than us.

"We could score points on some occasions, so I keep everybody under pressure to be there when the chance pops up.

"We will be pushing like hell – as if we were fighting for the championship."