Top teams Ferrari and Mercedes are pushing back against Liberty Media's plans to modernise Formula 1.

Ferrari are threatening to quit the sport after new F1 owners Liberty announced their intention to substantially change the engine rules for 2021.

Former F1 supremo Bernie Ecclestone thinks that the threat is real.

"If the regulations come out where Ferrari think it is going to be a struggle and they can't support the money then they will leave," he told The Independent.

The top two teams are also set to hit back against the plans for a €100-€150m (£89m-£133m) budget cap.

Those plans are to be unveiled by Liberty Media early this week.

"We are curious to see what we are presented with," Mercedes boss Toto Wolff told Bild am Sonntag.

It is believed that, to police compliance with the cap, the proposal will involve FIA accountants being embedded within each F1 team.

However, Wolff insisted: "Nobody will get insight into our internal structures and processes."

Ecclestone thinks that Ferrari will also not accept a budget cap.

"They want to spend what they can afford to spend and I've always said the same thing. If people can't spend they have to go," he said.

Bild quoted Ferrari president Sergio Marchionne as saying that he is ready for a fight.

"I expect there to be a dispute until there is a solution," he said.

The 2017 championship continues this weekend with the Brazilian Grand Prix.