Cyril Abiteboul has admitted he is "worried" about the latest developments at Honda.
Some believe the next performance steps taken by the Japanese manufacturer will move the Honda power unit clear of Renault and close to Mercedes and Ferrari.
Renault is finally losing Red Bull as a customer at the end of this year, with the energy drink owned team to instead join Toro Rosso with works Honda power.
The McLaren-Honda collaboration was a disaster, but Renault boss Abiteboul admits that the latest signs from the Honda camp are that the most recent engine steps are really working.
"Yes, frankly I'm worried about everything in life, but in particular about a situation on the engine side.
"As we've seen since last year, Honda is making big steps, big gains," said the Frenchman.
'We have our way to do things'
"Red Bull has been very clear that they are investing massively, and apparently much more than us.
"We are happy for Red Bull and Honda but frankly we have our way to do things. We have a plan and we are executing that plan. It's not just about an arms race," Abiteboul admitted.
Renault has signed up Daniel Ricciardo but the Australian's 2019 teammate, Nico Hulkenberg, admitted recently that the works team has not made the progress expected this year.
But Abiteboul said Renault has a different task before it compared with the new Red Bull-Honda alliance.
"We have all the aspects of the package to develop. No one is providing anything to us, either in the powertrain or on the chassis, so it has to be step by step.
"We are very confident in our upgrade for next year. We want to play the long game," he insisted.