The ball is in Red Bull's court as the McLaren-Honda saga rolls on.
As the teams packed up in Monza, it seemed clear that McLaren and Honda were set to split.
"I'm still trying to get a good performance from us to convince them [to stay]," Honda's Yusuke Hasegawa said on Sunday. "But I'm not sure it will be enough."
"McLaren has always reached its targets. Honda have never reached theirs."
However, although believed willing to take a $100m (£77.3m) per year hit by cancelling its Honda sponsorship, McLaren cannot simply quit the deal as they need an engine supplier to switch to - and Mercedes, Ferrari and Renault are all fully-subscribed with three partner teams apiece.
McLaren are trying to convince Toro Rosso and their owner Red Bull to give up the Faenza team's customer Renault deal in order to keep Honda in F1.
"The situation is complicated because it's not just about McLaren," Boullier said.
"We also need to consider what is best for the whole of Formula 1. All parties to the negotiations understand this. I cannot tell you any more about it."
McLaren executive Brown said: "The ideal scenario is where everyone is smiling at the end.
"But to get there Toro Rosso has to play along.
"We need to know what we are doing and where we are going, because we're now in a timeframe that affects the design of the car for next year."
The 2017 championship continues in Singapore in a fortnight's time.