Pascal Wehrlein is linked with a return to formula one.
After losing his Sauber seat, the Mercedes junior returned to the German touring car series DTM for 2018.
But a rumour says Red Bull is interested in signing up the 23-year-old to replace underperforming Toro Rosso driver Brendon Hartley.
Bild newspaper claims the matter was discussed at the Spanish grand prix last week during a rare visit to the paddock for Red Bull magnate Dietrich Mateschitz.
Dr Helmut Marko said of the rumour : "I don’t know where it comes from."