(CNN) - The Formula One season is the longest it has ever been.
In 2018, for the second time in three years, drivers and teams have competed over the course of a 21-race season, spending more time away from families and homes.
Now, with the announcement of a Vietnamese Grand Prix being added to the calendar from 2020, Lewis Hamilton has expressed his concern that the season is becoming unbearably long.
"I am not going to be here if it gets to 25 races, that's for sure," Hamilton told reporters.
"It already feels like we are on race 25 this year, so I don't think that's a good thing. I think 18 was probably the best back in the day."
Despite next year also featuring 21 races, the schedule in 2019 means the F1 calendar will run into December for the first time in over 50 years.
Liberty Media, the company that has owned Formula One since January 2017, has often expressed its hopes of expanding the season further.
"I'm someone who really loves racing but the season is long," Hamilton said. "It's a lot of commitment for all of us and a lot of time away from families, and the seasons are getting longer and the off time is getting shorter.
"All I can do is speak is for myself. The turnaround is so short, you start preparing for your next season often as soon as the season is done.
"Getting your mind turned. That's very difficult. Then you have to find a way of switching off and recovering at the same time."
Hamilton wrapped up his fifth world title in Mexico a fortnight ago but the constructors' championship is still to be decided.
Ferrari must better Mercedes' score in Brazil this weekend by 13 points or more if they want the title race to go to the season finale in Abu Dhabi.
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