A circuit guide in the current style showing the layout and key stats about the Hanoi circuit that will debut in 2020. (1:50)

Formula One's commercial boss, Sean Bratches, has sent a warning to historic circuits such as Silverstone, reminding them that their position on the calendar is not essential for the sport's long-term future.

Following an announcement Wednesday that F1 will go racing in Vietnam from 2020, questions about the future of existing races have been raised. The contracts for Silverstone, Hockenheim, Monza, Barcelona and Mexico City are all due to expire at the end of the 2019 season, and Silverstone and Monza have made no secret of their desire to see a reduction in the sanctioning fees they pay F1.

Race fees are a key source of income for F1, and the sport's owners, Liberty Media, have discussed the possibility of expanding the calendar to 25 races to increase revenues. However, plans to add a Miami street race in 2019 fell flat earlier this year and have since been postponed indefinitely, while the majority of teams are against expanding the calendar beyond 21 grands prix.

Negotiations with Silverstone over the future of the British Grand Prix have been taking place for more than a year, since the circuit announced in 2017 that it would trigger a break clause to make the 2019 race the last of its current contract. The circuit has made clear that it wants to continue in F1 but will do so only on terms that ease the financial burden of hosting the race.

Silverstone's hand has been strengthened by several public statements from F1's bosses promising they would preserve "heritage races," but Bratches has revealed that the sport is not afraid of replacing some of its most iconic venues.

"We're a 68-year-old entity, and the nature of grand prix racing is that it is dynamic," he said in an F1 news release. "Silverstone was the first grand prix, but we haven't raced at Silverstone all those 68 years. The race has been held at Brands Hatch and other venues. Nothing is immutable in this sport in terms of where we race.

Sean Bratches heads up Formula One's commercial operations. CHRISTOPHE ARCHAMBAULT/AFP/Getty Images

"We do value certain races highly, and we do what we can to preserve racing there, but we are a business. We are a public company, and we have a lot of stakeholders and shareholders, and we're trying to marry what's best for fans with running a successful business."

Bratches explained that he wants to see a mix of circuit types on the calendar, with an emphasis on growing the number of street races, such as the proposed circuit in Vietnam's capital Hanoi.

"We look at it in three ways," he said. "Firstly, we want to preserve the heritage races. They are very important to Formula 1, and they are very important to fans. I'm talking about the Silverstones, the Spas, the Monzas of this world.

"Then we have a set of street races and hybrid street races, where we race in parks and on city streets, such as Melbourne, Montreal and Mexico City.

"The third segment features purpose-built facilities such as Shanghai, Austin, Texas, and Bahrain. Beyond that, we are looking to identify further street races, so this race is a further step in terms of our vision."

Bratches envisions more races in cities such as Hanoi and said F1 is carefully considering where to go next based on a number of offers from around the world.

"One of the things we have been intensely focused on is extending grand prix racing to iconic cities, in downtown areas, where we can best engage fans," he said. "Most of our grands prix are currently half an hour to an hour outside cities, so the race in Hanoi fulfills of one of our preliminary goals -- an iconic city hosting racing on a potentially thrilling street circuit. Vietnam's concept of what grand prix racing should be about matches our vision for the sport.

"We're the beneficiaries of interest from cities, states, countries, municipalities from around the world, and we have been taking a very cadenced approach in terms of how we go to market in terms of race promotion, choosing carefully so that potential races fit well with the existing structure we have and the direction in which we want to go in the future

"Historically, Formula One has been very reactive in terms of people coming to them, but we have been more proactive, going to markets that we think are aligned with our brand values and which provide the opportunity to engage fans in new ways. A street circuit is a great way to do that. We have Monaco, Baku and Singapore, and this is a great addition to that lineup."