Red Bull team principal Christian Horner fears McLaren is "a few tenths" too quick for any of its rivals in Bahrain, with a repeat of Max Verstappen's outstanding Suzuka victory unlikely.
Oscar Piastri topped McLaren team-mate Lando Norris in Friday's second practice session, with the pair half a second clear of Mercedes' George Russell and Ferrari driver Charles Leclerc.
Having sat out FP1 to give Red Bull reserve Ayumu Iwasa an outing, Verstappen was seventh – eight tenths behind – with Yuki Tsunoda down in 18th after conducting set-up experiments.
According to team boss Horner, McLaren is a class apart this weekend as the hot and abrasive Bahrain circuit looks set to favour the papaya squad.
"We've got quite a bit to do tonight, I think," Horner told Viaplay. "The McLarens look very, very quick. With Mercedes and Ferrari it all looks pretty close, but McLaren definitely look like they have a few tenths on the rest of the field.
"First of all, we've got to understand how we can improve what we have, which is mainly temperature-related, I think."
Red Bull overhauled its set-up last weekend in Japan after a similarly difficult Friday to give Verstappen a shot at taking an outstanding pole, but Horner fears Bahrain's more abrasive layout will reward McLaren's better tyre usage and make it harder to keep faster cars at bay in the race.
"It is impossible to repeat what he did last week over a single lap and then holding the cars behind for an entire grand prix," Horner cautioned. "This is a track you can overtake at relatively easily, so a lot of work to do with the engineers tonight."
Not just engine modes
Speaking to Autosport, the team's advisor Helmut Marko painted a similar picture, and while Red Bull tends to run with less powerful engine modes in practice he said the squad's deficit went well beyond that.
"We are too slow and the tyres are becoming far too hot," the Austrian said. "It's basically confirming what Max already said yesterday, that Bahrain will be a more difficult one for Red Bull.
"The main problem is the tyre temperature, which we can't keep under control. And as soon as the temperature goes up, we are sliding, which makes it worse.
"Strangely enough, at one stage the tyre recovered and we were doing the same lap times as Lando, but that was only three or four laps out of 15. This track just doesn't suit us and neither do these high temperatures."
