Vettel won his four consecutive championships with Red Bull between 2010 and 2013, and came close to winning further titles with Ferrari after he joined the Maranello squad in 2015.
Now, according to Marko, the 36-year-old has been enquiring about returning to the Milton Keynes-based squad and replacing Sergio Perez.
Speaking with Formel1.de, the Austrian said: “Vettel has repeatedly enquired with us, but I don’t think it would be pleasant for him to drive next to Max Verstappen.”
Perez was retained by Red Bull for 2024 after he secured the team’s first one-two finish in the world championship last year, but has been under increased pressure to keep his seat for 2025.
Since 2018, the Dutchman’s previous team-mates in Daniel Ricciardo, Pierre Gasly, Alex Albon and now Perez have struggled to compete with him and it is likely to be no different if Vettel was to get the drive.
“If I’m correctly informed, he seems to be moving towards Porsche and long-distance racing. I think that would be a very nice step for him,” added Marko.