Dr Helmut Marko thinks Max Verstappen could have a fight on his hands next time out at Red Bull's home Austrian GP.
World champion Verstappen continued his run of dominance in Montreal, but it was a much closer affair with fellow champions Fernando Alonso (Aston Martin) and Lewis Hamilton (Mercedes) also on the podium.
And Germany's Auto Motor und Sport says wind tunnel and simulator data produced by Aston Martin shows that next series of upgrades could draw the team level with Red Bull.
"We will only be able to optimise the package in Austria and Silverstone," Spaniard Alonso said.
"There is more to come. I really want to win a race."
Aston Martin boss Mike Krack agrees: "The improvements work and we are not going to stop.
"We are in a good place, but we are not going to settle for that."
Marko, meanwhile, said that while Alonso and Hamilton came closer to the top step of the podium in Canada, it was actually the Ferraris with the strongest race pace.
"Let's see," the top Red Bull official, 80, told Osterreich newspaper on Wednesday.
"In Montreal, Ferrari had the fastest car. And now the Red Bull Ring suits them.
"If (Charles) Leclerc starts from row 1 or 2, it won't be a walk in the park for Max."
Publicly, however, Dutchman Verstappen does not seem worried that Aston Martin, Mercedes and Ferrari have all made strides forwards with updates recently.
"The car has been fast and nice to work with from the start. There are no mysteries with it so that helps a lot every weekend," he said.
"We are not worried at the moment, but the other teams are improving with many updates. We are still ahead, but we have to keep working.
"But I don't think I need to say that. Things (updates) are coming," Verstappen is quoted by the Spanish newspaper El Mundo Deportivo.
"Canada was complicated due to the temperatures. We couldn't get the tyres to work. But winning by 9 seconds shows that we still have a good car."
