Hulkenberg, who is in the running to replace struggling Alex Albon next year, joked on Red Bull-owned Servus TV this week that he has now "signed a new contract".
"A home loan contract," he grinned. "I hope I get a good return."
Marko, the head of Red Bull's famous driver program, has said he will make a decision about Albon's future after the Abu Dhabi finale next month.
As for Hulkenberg's contract joke, he told Auto Bild: "That was typical German humour."
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