Red Bull motorsport adviser Helmut Marko says he has "great concern" about Max Verstappen's future with the team in the context of their current struggles.

The four-time champion finished sixth in the Bahrain Grand Prix on Sunday, while Oscar Piastri scored McLaren's third win in four races so far this year.

Dutchman Verstappen is third in the drivers' championship, eight points behind leader Lando Norris of McLaren.

Marko told Sky Germany: "The concern is great. 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."

Verstappen has a contract with Red Bull until 2028. But Marko told BBC Sport this month that it contains a performance clause that could allow him to leave the team.

The wording of this clause is not known publicly but it effectively says that Red Bull have to provide Verstappen with a winning car.

Verstappen won the Japanese Grand Prix a week before Bahrain but that victory was founded on a pole position lap that many F1 observers regarded as one of the greatest of all time.

Because overtaking was next to impossible at Suzuka, Verstappen was able to hold back the McLarens of Norris and Piastri and take his first win of the year.

Verstappen has qualified third, fourth and seventh for the other three races in Australia, China and Bahrain.

The Red Bull is on average over all qualifying sessions this year the second fastest car but 0.214 seconds a lap slower than the McLaren.

Verstappen has complained all year about balance problems with the Red Bull, which is unpredictable on corner entry and has mid-corner understeer.

Red Bull team principal Christian Horner admitted after the race in Bahrain that the car's balance problems were fundamentally similar to the ones that made the second half of last year a struggle for Verstappen.

He won just twice in the final 13 races of last season, but managed to win his fourth world title because of the huge lead he built up when Red Bull were in dominant form in the first five races of the season.

Horner also said the team were having difficulties with correlation between their wind tunnel and on-track performance. Essentially, the car performs differently on track than the team's simulation tools say it should.

Verstappen had a difficult race in Bahrain including delays at both pit stops, one with the pit-lane traffic light system and one with fitting a front wheel.

At one stage he was running last, and he managed to snatch sixth place from Alpine's Pierre Gasly only on the last lap.

Verstappen said that the hot weather and rough track surface had accentuated Red Bull's problems.

He said: "Here you just get punished a bit harder when you have big balance issues because the Tarmac is so aggressive.

"The wind is also quite high and the track has quite low grip, so everything is highlighted more.

"Just the whole weekend struggling a bit with brake feeling and stopping power, and besides that also very poor grip. We tried a lot on the set-up and basically all of it didn't work, didn't give us a clear direction to work in."

Verstappen has said this year that he is "relaxed" about his future.

Any decision about moving teams for 2026 is complicated by the fact that F1 is introducing new chassis and engine rules that amount to the biggest regulation change in the sport's history, and it is impossible to know which team will be in the best shape.

But it is widely accepted in the paddock that Mercedes are looking the best in terms of engine performance for 2026.

Mercedes F1 boss Toto Wolff has made no secret of his desire to sign Verstappen.

The two parties had talks last season but have yet to have any discussions this season about the future.