Helmut Marko has admitted that Mercedes and Ferrari look "clearly faster" than Red Bull after Friday practice at the Canadian Grand Prix.
Red Bull arrived in Montreal looking to claim their 100th Formula 1 victory, having won each of the first seven races of the 2023 season.
However, the reigning Constructors' Champions seemed to struggled on the opening day of running at the Circuit Gilles Villeneuve.
Max Verstappen - searching for a fourth consecutive win this weekend - could only manage sixth place in FP2, while team-mate Sergio Perez was a distant eighth and slower than Alfa Romeo's Valtteri Bottas.
Perez also appeared to brush the wall at one stage during the afternoon session, which was extended by 30 minutes after FP1 was interrupted by the after-effects of a local power cut.
Although the high-speed nature of this track was expected to suit the RB19 car, renowned for its fearsome performance on the straights, Red Bull advisor Marko says he is concerned by the displays of both Ferrari and Mercedes on Friday after both teams introduced major upgrade packages in recent weeks.
And, in particular, he is alarmed by a long run by Charles Leclerc that suggests Ferrari can at least match the Red Bulls in race conditions.
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"I think the gap is a bit confusing," Marko told ServusTV, as quoted by Motorsport-Total.
"The track became much faster towards the end. That's when we did a long run.
"But nevertheless: we have some work to do in the car. The car is too unsettled. The long run was a bit better, but Leclerc was also very fast - or at least as fast as us. So, some work to do.
"We are all expecting that 100th win and apparently that has caused extra pressure. So we were a bit surprised that we were a bit off internally, especially in terms of handling.
"[Mercedes have become] clearly faster, but I fear that Ferrari will be even stronger here. You could see that. They were out at about the same time as us. And especially Leclerc's long run was very impressive."
While Lewis Hamilton and George Russell completed a Mercedes one-two in FP2, it should be noted that both drivers set their fastest laps much later in the session than many of their rivals and when the circuit was at its quickest.
As others pursued fast laps in the first half of the session, Hamilton and Russell were rooted at the bottom of the leaderboard for some time as Mercedes focused on high-fuel runs on the medium tyres.