Formula 1 may not get any new teams on the grid until 2022 at the earliest, sporting boss Ross Brawn said at Spa.
Brawn said it might be better to see the impact of sport's new era in 2021 before opening the paddock gates to any new competitors.
The comments follow reports that a new Silverstone based team called Panthera is hoping to debut in 2021.
When asked if the existing teams would welcome newcomers, Renault boss Cyril Abiteboul said at Spa: "If it's good teams, strong teams with good backing, then it's a sustainable project in my opinion, so yes."
Toro Rosso's Franz Tost agreed: "I would welcome them."
However, Haas owner Gene Haas has said on a couple of occasions in recent days and weeks that the American team's presence beyond 2020 is not guaranteed.
"What FOM needs to look after is the teams that are here," said Haas team boss Gunther Steiner. "Just thinking more is better will not work as well."
