Fernando Alonso has indicated he will leave McLaren-Honda at the end of the year if he does not see signs they can be competitive by September.
The two-time world champion is out of contract at the end of this season.
“We have to win,” he said. “If we are winning before September, when I will make a decision, I will stay.”
When pointed out this was unlikely, he said: “I joined this project to win the title. If you are not in a competitive position, maybe you change project.”
However, the Spaniard said he had not yet started to think seriously about his future.
“Until I sit down with myself in September, I cannot say for sure,” Alonso said.
Alonso joined McLaren at the start of 2015, when they began their relationship with engine partner Honda. But the team have been uncompetitive for all three years, largely because of a lack of performance from the Honda engine, and that is causing tension within the team.
McLaren executive director Zak Brown said on Wednesday that he had “serious concerns” about Honda, which he said appeared “lost”.
He added that the McLaren-Honda relationship was nearing “a fork in the road” and that McLaren were “not going to go into another year like this, in hope”.
Alonso said: “We all want to win and Zak’s comments about Honda is what you would expect him to say. He wants to win, he wants McLaren to win and things have to change.”
Are McLaren and Honda set to split?
Brown’s remarks signal a shift in McLaren’s public position on Honda, which had previously been that they are “100% committed” to the relationship.
Until recently, senior figures were briefing that McLaren would definitely stick with Honda in 2018 but the ground appears to have shifted and there are growing indications that they may split.
In that circumstance, McLaren would seek to try to secure a deal for Mercedes customer engines, which would almost certainly provide a competitive boost.
However, it would affect the team’s financial position as the Honda deal equates to a net $100m gain for McLaren over using a customer engine because the Japanese car manufacturer not only provides free engines but also pay half the drivers’ salaries and contribute a significant amount of sponsorship.
What are Alonso’s options?
McLaren want to keep Alonso in 2018 but if they switched to customer engines would not be able to afford to offer him his current salary of $40m a year.
However, he appears not to have too many options. Mercedes, Ferrari and Red Bull are considered unlikely to want to sign him and while Renault is keen, it also could not afford to pay him anything like the amount of money he is earning this year.
Alonso, who missed the last race in Monaco to compete in the Indianapolis 500, said his main intention was to stay in F1 next year.
“In F1, the third world championship is still my biggest priority,” he said. “I developed my skills to drive F1 cars for 16 years so it is the best car I can drive.”
But he said his performance at Indy, where he led several times and was contending for the win in the closing stages only for his engine to fail, had encouraged his belief that he could win there and at Le Mans in the future.
“I jump in any car in any categories with any tyres and rules, I go there and I am competitive,” he said. “I am not afraid of the future. If I cannot win the third world championship here, I will race in any series and know I can win.”