Sebastian Vettel returning to Red Bull is a prospect that has been all but ruled out by Christian Horner after the four-time world champion confirmed he will leave Ferrari.
Red Bull team principal Horner worked with Vettel for each of his Formula One drivers' championships between 2010 and 2013, which came as part of six total seasons with the team.
Max Verstappen is established as the number one driver, though, and following his decision to sign a new contract until 2023, Horner is reluctant to pair him with another "alpha male" when Vettel becomes available in 2021.
Alex Albon was promoted from Toro Rosso to partner Verstappen midway through last season and the team like what they see so far.
"It's enormously unlikely," Horner said to Sky Sports about the chances of Vettel returning. "We have a long-term agreement with Max, and I think Alex is doing a good job.
"We've got a good dynamic within the team and experience shows that two alpha males doesn't tend to pan out well.
"Sebastian is still a very competitive grand prix driver, so I don't think it would be conducive for our team to have two alphas.
"We're happy with the driver line-up we have. I'm sure he's not short of options moving forward, but obviously he's chosen it hasn't worked out for him at Ferrari."
Horner is unsure what Vettel will do next, with Renault and McLaren seen as his most likely landing spots should he decide to remain in F1 beyond 2020.
Mercedes team boss Toto Wolff has also said he will take the development into consideration, though a move to Ferrari's rivals is seen as unlikely, with retirement also a mooted possibility.
"I'm sure he's thought long and hard about it, and you have to respect his decision," added Horner.
"Where he goes to from here, I have no idea. But he's a guy with great integrity, great principles and whether he chooses to continue or not, he's achieved obviously a huge amount in his time in Formula One.
"Four world championships, he's one of the most successful drivers of all time. He's still relatively young, he's in his early 30s, if he chose to stay, he's obviously still very competitive.
"That's entirely down to him and nobody will know other than Sebastian what his choices are."