Honda chief Yusuke Hasegawa wants Sauber to confirm its 2018 plans as soon as possible, with doubt still hanging over their agreed partnership.
During the Russian Grand Prix weekend Sauber confirmed a deal to take Honda engines for 2018. Former team boss Monisha Kaltenborn was the architect behind the deal, but her departure has led to speculation the deal is off.
Frederic Vasseur, who replaced Kaltenborn, has put the Honda issue top of his list of priorities but the situation remains uncertain. Honda says if cannot afford to wait too long to hear that decision.
When asked when Honda needed to know if the deal was going ahead from a planning point of view, Hasegawa told Racer: "Now. As soon as possible. We cannot wait for next year's preparations so we are working on it already and we really need to fix [a decision].
"From the plan point of view we are already working on [being ready for the Sauber supply in 2018]. So we need to fix the plans, but we will just continue as we are for now. So far, no change."
If the deal goes ahead, Sauber would join McLaren as a Honda engine partner. Honda has struggled since returning to F1 in 2015 and has produced three consecutive uncompetitive engines.
Sauber is running a year-old Ferrari engine this year, a decision taken so new owners Longbow Finance could focus on restructuring the team in 2017.
It is believed Longbow have reservations about the Honda deal, with a supply of up-to-date Mercedes and Ferrari engines also available.