Ferrari supplies Haas with spare parts teams that do not need to be designed and built, while Red Bull's junior team Toro Rosso will use many components from last year's RB14.
In addition to these examples called "B teams," there are concerns that large teams could be supported by their engine customers or partners who contribute R & D resources.
The FIA has previously indicated that this will be closely monitored as F1 prepares to introduce a cost cap and other resource constraints for 2021.
Asked by Motorsport.com if there is a danger of joining smaller teams, Renault F1 CEO Cyril Abiteboul said: "We could spend hours discussing this topic.
"It's already a challenge for a team like us to compete against the top three teams who have about 30% more resources than we do.
"If they are able to combine their resources with other teams or leverage synergies within a budget cap, this is a problem for us and for at least two other teams on the ground."
This is a reference to McLaren and Williams, who joined Renault last year when they initially refused to approve Racing Point by retaining the commercial rights of Force India when the team from Silverstone fell into the administration.
This was in the midst of fears that Racing Point would get closer to Mercedes.
Abiteboul said Renault was dissatisfied with the response he received from the rulers on dealing with the situation for 2021 and warned that "it could be a problem for a newcomer willing to participate in F1 and ready is to be competitive ".
"This is a serious issue because we may say that there are three top teams and that it will be," he said. "Perhaps everyone who joins must accept that he is unable to compete.
"We are extremely careful about what we want to do in 2021. We are not convinced of the protective measures and mitigation measures that have been introduced.
"We will continue to work with the governing bodies to hopefully achieve a more satisfactory result."
On the same question as Abiteboul, Christian Horner, Red Bull team principal and Ferrari boss Mattia Binotto answered that they support the current F1 model.
They said it was the small teams that benefited from such arrangements, with Haas being mentioned as a prime example.
"The affordability of Formula One is extremely expensive," said Horner.
"Ultimately, there is a reasonable tradeoff between the need to be a mature constructor team and to be able to acquire those unlisted parts."
Binotto said "the model itself is the right model" and is a good thing for F1.
He added, "If there are any concerns, it is up to us to understand what they are and to make sure we mitigate or avoid them."