Four-time Formula 1 world champion Sebastian Vettel has expressed his concern over the possible expansion of the calendar beyond 20 races in the coming years.

2016 was the longest season in F1 history, featuring 21 races and running from mid-March to the end of November.

While 2017 sees the schedule fall back to 20 rounds following the cancellation of the German Grand Prix, new F1 owner Liberty Media is thought to be planning a rapid expansion in the coming years that could see the calendar swell to as many as 25 races.

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However, Vettel is uneasy about such a move, saying it places a huge amount of pressure on the team personnel and may cause burn-out.

"25 is too many. I think 20 is enough, we don't need more," Vettel said. "I think anything between 16 and 20 is the right number. I think for us [drivers] it's fairly easy, arriving more or less with hand luggage. But for the team and staff it's hard work. So I think we are having enough races."

Vettel's view was not shared by rivals Daniel Ricciardo and Lewis Hamilton, both of whom were receptive to the idea of expanding the calendar and getting more racing in each season.

"I think it depends how they structure it. It's not too many," Ricciardo said. "NASCAR does 36 and it's a lot, but the travel's a lot less. I think it depends logistically how they do it. I like racing. If it means more racing and less testing and other stuff, maybe. We spend more days in front of cameras and other things than in a race car, so if that changes, I'll be open to the idea."

Hamilton added: "I think if you ask any member of my team if they want more or less races, they'd say more. They're addicted to it. I love racing, so I'm not opposed to more races, but they've got to change the structure for weekends.

"If it's the same four days for 25 races, I think it'll be too much."If they spice it up and make a period during the season that's a more exciting than perhaps the other, I think there's a lot they can do."