Momentum is continuing to build behind the idea that Lando Norris could become Max Verstappen's next teammate at Red Bull.
The duo are friends, and world champion Verstappen suggested at Monza that only Briton Norris' long McLaren contract is a barrier.
"Look, Lando is a great driver, there's no doubt about that, and you can see his potential is growing," Red Bull team boss Christian Horner said ahead of the Italian GP.
"But he's a McLaren driver and you have to respect the agreements that are in place."
One of those agreements is Sergio Perez's, who has a deal to remain at Red Bull next year - even though Marko insists it's not a "job guarantee".
"In '25, we have one seat open and as you can imagine, there's not a shortage of interest in that seat," Horner said.
Speaking to Kleine Zeitung newspaper, Marko said Norris' existing McLaren contract runs until 2025.
"But he is by far the strongest of the young drivers," said the Austrian.
"His youthful nature would also suit him to Red Bull. We were close to signing him to Alpha Tauri, but that was a few years ago," Marko revealed.
"At that time it also failed because of ongoing contracts."
When asked if Red Bull might be willing to buy Norris out of his McLaren deal, Marko answered emphatically: "No, that is completely out of the question.
"Sergio Perez is currently fixed."
