Fernando Alonso says he has given struggling McLaren until October to persuade him they can provide a winning car next year or else he will talk to teams that can.
The dual Formula One world champion, preparing for his home Spanish Grand Prix, failed to start in Russia last month because of engine failure, a situation he described as "totally unacceptable".
McLaren have not won a race since 2012, and have struggled for performance and reliability since entering a new partnership with Honda in 2015.
Meanwhile, Alonso will be 36 in July and can sense time ebbing away.
"My intention or first priority is to race next year here and not only to race, I want to win," said the Spaniard, who is out of contract at the end of the year.
"I am happy with the team, but we are not winning."
"If from here to September/October we are in a position that I see clearly a possibility to win in 2018, I will be more than happy to stay with the team.
"If it is not the case then I will be more than happy to talk to anyone."
McLaren are yet to score a point in four races, Alonso is missing Formula One's showcase Monaco Grand Prix on May 28 in order to compete at the Indianapolis 500.
Alonso says he would also have to consider whether "it was time to find other challenges outside Formula One", though he said he liked the 2017 specifications that gave cars a higher cornering speed.
He has spoken of his desire to become only the second driver ever to win the Triple Crown, which would mean adding victory at Indianapolis and the Le Mans 24 Hours to the F1 titles he won with Renault in 2005 and 2006.
He says he still did not know what had happened in Sochi when his engine failed on the formation lap. That incident followed a no-start for Belgian teammate Stoffel Vandoorne in Bahrain.
"There are some things we need to put in place, starting this weekend, for the rest of the season. Hopefully this is the starting point of a new championship for us," said Alonso.
"We need to raise our game here in terms of reliability and hope to finish with both cars."