Red Bull's Daniel Ricciardo has left the door ajar to join Lewis Hamilton at Mercedes next season.
The Australian driver is Formula One's hottest property after he produced an overtaking masterclass to storm to victory in China a fortnight ago and he's 9/1 to go in again in Azerbaijan this week.
Ricciardo, 28, is out of contract at the end of the year, and while Red Bull are keen to retain his services, he is set to have the pick of the sport's top three teams for 2019.
Despite qualifying ahead of Hamilton at both of the past two rounds, Valtteri Bottas could be moved on from Mercedes at the end of the year, while Kimi Raikkonen's future at Ferrari is also unclear.
A move to Ferrari would see Ricciardo once again join forces with Sebastian Vettel, who he out-performed during their one campaign together at Red Bull back in 2014. Vettel subsequently left to join Ferrari.
"I would love to be challenged against the best and Lewis is arguably up there," said Ricciardo ahead of this week's Azerbaijan Grand Prix.
"I've got a good challenge now obviously with Max [Verstappen] and I had Seb, too, so I don't want to say it's just Lewis I'm looking for, but that would be a good challenge."
Ricciardo is likely to wait until the summer break before making his decision with Mercedes understood to be willing to give Bottas the first half of the year to prove his worth.
Mercedes are open to the idea of pairing Ricciardo with Hamilton and would not anticipate a repeat of the intra-team fireworks that overshadowed Nico Rosberg's time alongside the Briton.
At Ferrari meanwhile, Raikkonen has proved to be the perfect deputy for Vettel, but the veteran Finn turns 39 in October. Ricciardo, who claims to have spoken only to Red Bull about his plans for next year, insisted here on Thursday that he would only consider a move to the Italian giants on equal terms.
"I would always make sure that there was some clarity," Ricciardo added. "I wouldn't want to go somewhere where I didn't feel I had a chance.
"At the moment what I'm chasing is to try and be world champion. That's my goal, my dream, and something I really believe I'm capable of, so if someone said 'we'll let you come here but you can't do this', that's not an attractive option to me."
Hamilton meanwhile, had planned to put pen to paper on his new Mercedes contract before last month's opening race of the season in Melbourne.
But as he prepares for the fourth round, winless and nine points adrift of championship leader Vettel, the 33-year-old Englishman is yet to agree terms.
"I am fully committed to Mercedes," Hamilton said. "I have every plan to be with the team for the future. It is not a rushed thing. I have made it clear and they have made it clear that we will continue.
"Neither of us have the personality to say I am definitely going to be with you next year and then not commit."