Concern is growing within Red Bull that Max Verstappen will leave the team at the end of the year, according to motorsport adviser Helmut Marko.
After winning the Japanese Grand Prix one week ago, Verstappen could only finish sixth at Sunday's Bahrain Grand Prix amid issues with his car's balance and brakes.
Although he is still just eight points off championship leader Lando Norris in the drivers' standings, Verstappen has made no secret of his frustrations with his car's performance.
The 27-year-old has a contract with Red Bull until the end of 2028, but Marko revealed earlier this year that performance clauses exist that could allow him to exit early.
Asked by Sky Germany after the race in Bahrain if concerns were growing that Verstappen could leave at the end of the season, Marko said: "The concern is great. As I said, improvements have to come in the near future so that he has a car with which he can win again.
"We have to create a basis with a car so that he can fight for the world championship."
The crux of Verstappen's complaints focus on a handling imbalance with the car, which makes it hard to predict through corners and puts extra strain on the tires, leading to excessive performance degradation compared to his rivals during races.
The nature of the Bahrain circuit, which is particularly hard on tires, exposed the issues more than any other venue so far this season. After winning by 22 seconds at the same track last year, Verstappen said he believes Red Bull has taken a step backwards over the past 12 months.
"I just feel like we are even worse on tires somehow this year [compared to 2024]," Verstappen said. "It makes it just very complicated.
"Because last year we were not too bad around here [Bahrain]. Of course, then people made improvements, but I feel like we actually had a worse weekend than last year. So it's a bit weird."
Red Bull team principal Christian Horner admitted the car's key weaknesses had been exposed in Bahrain, whereas Verstappen's sensational qualifying performance in Japan one week ago had provided a workaround in the race.
"I think ultimately you can mask it a little through setup and we were able to achieve that last weekend in Suzuka," Horner said. "But I think this race has exposed some pitfalls obviously very clearly that we have that we need to get on top of very quickly and I think we understand where the issues are, it's introducing the solutions that obviously take a little more time."
Similar issues have been evident with Red Bull since last year, and Horner said a lack of correlation between the results the team is finding in the wind tunnel and the reality of the car on track has hindered a solution.
"I think the problems are understood," he said. "The problem is how the solutions that we see within our tools compare to what we're seeing on track at the moment -- they aren't correlating and I think that's what we need to get to the bottom of.
"Why can we not see within our tools what we're seeing on the circuit, and when you end up with a disconnect like that, you have to obviously unpick it. We've got a strong technical team that have produced some amazing cars over the last few years, and I'm confident they'll get to the bottom of this issue. But it's literally the tool isn't replicating with what we're seeing on the track, and then it's at that point it's like telling the time on two different watches."
Verstappen has been linked to moves to Mercedes and Aston Martin in the past year, but earlier this year he claimed no talks had taken place with the latter.