German motor racing legend Hans-Joachim Stuck thinks there is a risk that Formula 1's top teams will threaten to quit the sport.

The ten teams are not only yet to sign the 2021 Concorde Agreement, it has also emerged that the published 2021 regulations are effectively a draft.

"What is written down on paper is a starting point," confirmed F1 sporting boss Ross Brawn.

In the past, top teams regularly threatened to quit the sport when sweeping new rules or regimes were proposed.

"I hope it doesn't come to that," Stuck told Germany's Sport1.

"But when one of the teams says 'We'll leave', then they should leave," he added. "You can't please everyone, and another team will come."