Jacques Villeneuve does not think Red Bull-Honda can win the 2020 title.
A lot is riding on the team's performance next year, as Max Verstappen will be out of contract and Honda is yet to commit to F1 beyond 2021.
Outspoken 1997 world champion Villeneuve says Red Bull has a "great car", but he questioned the improvement Honda has made this season.
"Honda is not on the same level because they cannot manage to do seven races with just one engine," the Canadian told Germany's motorsport-total.com.
Villeneuve said that if Honda did manage to stick with F1's long-life engine rules, "they would have less power".
But Verstappen admitted to Algemeen Dagblad newspaper that Red Bull-Honda must come out of the blocks strong in 2020, rather than have a big mid-season surge.
"That cannot happen anymore," he said. "We have to be there from the start, not from the summer or the end of the season. From race one," he said.
"Everyone here is well aware of that."
But Verstappen is backing his team to be able to win the title in a "very important season" for Red Bull.
"They've proven it in the past, so it's not wishful thinking," he said. "That's why I'm with this team, even though it will not be easy."
Dr Helmut Marko is also sounding very bullish about 2020.
"We stayed below our potential this year," he told Kronen Zeitung newspaper. "The five wins would have been possible."body check tags ::