Australian Daniel Ricciardo looked set for a move to Renault after Red Bull announced on Friday that he would be leaving them at the end of the Formula One season.
The surprise announcement will ripple through the driver market, with other teams set to shake up their line-ups as a consequence.
"Daniel Ricciardo has advised us that he is to leave the team at the end of the 2018 season," Red Bull said in a statement without saying where he was headed.
The winner of two races this season has been linked to Renault and McLaren in media speculation but the former, as a manufacturer team in fourth place in the championship, look a more desirable option.
There was no immediate comment from the French team.
"We fully respect Daniel's decision to leave Aston Martin Red Bull Racing and we wish him all the best in his future," said Red Bull team boss Christian Horner.
"We would like to thank him for his dedication and the role he has played since joining the Team in 2014, the highlights of course being the seven wins and the 29 podiums he has achieved so far with us.
"We will now continue to evaluate the numerous options available to us before deciding on which driver partners Max Verstappen for the 2019 season."
Ricciardo had been out of contract at the end of the year and was assessing his options, but any hope of joining champions Mercedes disappeared when they retained titleholder Lewis Hamilton and Finland's Valtteri Bottas.
Glamour team Ferrari have shown no obvious interest either, with Sauber's Monegasque rookie Charles Leclerc tipped to replace Kimi Raikkonen if the 38-year-old 2007 world champion is not kept on.
The extrovert Australian, a fan favourite with his permanent smile and thrilling overtakes, had indicated before the August break that he was set to stay at third-placed Red Bull and was just 'fine-tuning' details.
Former champions Renault are the best of the rest and had a vacancy, with Spaniard Carlos Sainz there on loan from Red Bull alongside Germany's Nico Hulkenberg.
Sainz could return to the Red Bull fold alongside his former Toro Rosso team mate Verstappen but has also been linked to McLaren, where he could form an all-Spanish line-up with Fernando Alonso.
McLaren have not won a race since 2012 and are going through a rebuilding phase.