German Vettel, F1's reigning triple world champion and the 2013 title leader, has in the past been linked with a move to Ferrari.
And the most recent rumour is that Mercedes' Niki Lauda has made approaches to the 25-year-old.
Vettel, however, remains under contract to Red Bull, even if his boss Christian Horner told Sport Bild: "What team wouldn't want Sebastian Vettel?
"He has been part of the Red Bull family for a long time, and he's an important part of our success. We have steadily developed along with him.
"The issue is not so much about the length of contracts, but how comfortable you feel with one another.
"Seb feels comfortable with us, and we're comfortable with him. And I have no doubt that will be the same for a very long time into the future," he added.
"Seb is fantastic, but I don't think we've seen the best from him yet," said Horner.