Up to four or more engine suppliers may be interested in joining Formula 1 in 2021.

Despite early opposition from Mercedes and Ferrari, the sport's new owners intend to introduce a cheaper, louder and simpler engine formula after the current era ends in 2020.

BBC Sport reports that Ilmor and Cosworth, two independent engine manufacturers familiar with F1 in the pre-'power unit' unit, are interested in the 2021 rules.

"The new proposal makes it possible for an independent or existing car company," Cosworth chief Bruce Wood confirmed.

Red Bull sponsor Aston Martin is also eyeing the post-2020 engine rules, while Germany's Auto Bild claims that Porsche could enter the sport as well.

However, retired Porsche sports car driver Mark Webber insisted: "Porsche in Formula 1? It will not happen."

As for McLaren boss Zak Brown, he admitted that he hopes the 2021 rules succeed in tempting more engine makers into the sport.

"It would be great to have an independent engine or two, so that if you aren't in a situation where you have a manufacturer, you still have economical and yet still competitive options," he said.

The current championship continues with the Brazilian Grand Prix on Sunday.