Vettel's last outing in F1 came at the final race of the 2022 season, at the end of a disappointing spell with Aston Martin.
He had previously been the sport's dominant force, winning four drivers' titles at Red Bull between 2010 and 2013, before spending six frustrating seasons with Ferrari.
Is Vettel running out of options for F1 return?
Earlier this year, the 37-year-old strongly hinted he would be open to getting behind the wheel once again, admitting that conversations had taken place with Mercedes boss Toto Wolff among others in the paddock over any potential openings.
Sauber - who will transition to Audi in 2026 - have emerged as contenders in recent months, with the team eager to complete their driver line-up having already secured the signing of Nico Hulkenberg on a multi-year deal.
Speaking to Sky Germany at last weekend's Italian Grand Prix, however, former Williams driver Ralf Schumacher refuted suggestions that the German outfit would be keen to bring Vettel on board.