Five-time world champion Lewis Hamilton has threatened to quit Formula One if organisers keep adding races to an already congested calendar.
Hamilton secured his latest drivers' title with a fourth-placed finish in Mexico last time out, the 19th stop of the 2018 campaign.
Brazil and the United Arab Emirates are the final two races of the season, the latter coming on November 25, eight months after the curtain-raiser in Melbourne.
The 2019 schedule also has 21 races but will run from mid-March to early December, while owner Liberty Media is keen to add further grands prix.
In 2020, the first Vietnam Grand Prix will take place, while there have been suggestions an extra race in the United States – in Miami – could be added.
Hamilton is not a fan, though, and has suggested he would leave the sport should further additions be made.
"I am not going to be here if it gets to 25 races, that's for sure," said the Mercedes ahead of the Brazilian Grand Prix.
"It already feels like 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.
"I'm someone who really loves racing but the season is long. 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."
|Guardiola eyeing future international job|
|Trubisky doubtful for Bears´ Thanksgiving game|
|O´Neill planning ´next adventure´ after leaving Republic of Ireland|
|Premier League: Brexit should not be used to weaken squads|
|16 balls, 14 boundaries, 74 runs - Shahzad steals show in T10 opener|
|WATCH: Patrice Evra plays with poultry in bizarre Thanksgiving message|
|Packers star Rodgers pledges $1m to California wildfire relief|
|Klitschko worried for boxing´s Olympic future|
|Lewandowski back in Bayern training as Davies joins new team-mates|
|Hogg fit for much-changed Scotland|
|Former Arsenal striker Bendtner faces 50 days in prison over taxi driver assault|
|Athletic extend Muniain contract to 2024|
|Kohli ready to move on after narrow defeat|
|PSG to wait for Neymar, Mbappe injury updates|
|Icardi hopeful of Messi return for Copa America|
|Cavs star Love expects to be out until 2019|
|Ricciardo terrified by Renault switch|
|Under-fire Taylor calls for PFA structure review|
|McLaren reveal one-off livery for Alonso´s last race|
|Samir Nasri training with West Ham amid reports of free transfer|
|Guardiola warned over derby clash comments|
|Stoinis sees Australia to T20 win against India|
|Modric not deserving of Ballon d´Or – Cavani|
|F1 Raceweek: Alonso ends on 312 races, Raikkonen a Ferrari great - Abu Dhabi GP in numbers|
|Neymar made a mistake leaving Barcelona for PSG, insists Edmilson|
|O´Neill and Keane leave Republic of Ireland after relegation|
|WATCH: Maxwell hits Spidercam with sliced shot in Australia-India T20|
|Rafinha wants Barca exit due to ´crazy´ Valverde selections – Mazinho|
|France to wear rainbow laces in support of Thomas following attack|
|You need to stop this – Cavani slams media over supposed Neymar feud|
|Anderson rested for final Test|
|Tite applauds Seedorf for Cameroon´s style of play|
|Griezmann not obsessed with Ballon d´Or|
|Neymar feels injury is ´nothing serious´|
|Durant says Green altercation won´t impact his free agency|
|Morris blasts drama surrounding Wizards: It´s messed up|
|Scaloni thrilled for Dybala, Icardi|
|Green´s last-second shot keeps Raptors atop East standings|
|Deschamps praises Griezmann for Giroud gesture|
|Warriors star Curry improving, still out at least three more games|
|Chile 4 Honduras 1: Sanchez, Vidal shine for La Roja|
|Argentina 2 Mexico 0: Icardi, Dybala score first international goals|
|Mickelson calls Tiger the greatest of all time|
|Durant fined $25,000 for using inappropriate language|
|Fizdale isn´t concerned about Knicks´ losing streak|
|No particular concern for Mbappe – Deschamps|
|PSG team-mate Choupo-Moting hopes Neymar injury is not serious|
|McLeish marvels at stylish Scotland´s promotion success|
|Draw proves Poland can play well without Lewandowski – Brzeczek|
|Giggs: Wales let themselves down|
|Sarachan ´moved USA forward´ in interim spell|
|Mickelson lays $200,000 bet with Woods for first hole|
|Dolphins QB Tannehill to start against Colts|
|Murcia edge out Banvit, Bonn crush Opava|
|Neymar injury not serious, says doctor|
|Mancini: Italy ahead of schedule|
|France 1 Uruguay 0: Giroud hits the spot after Mbappe injury blow|
|Portugal 1 Poland 1: Milik penalty salvages precious point as Danilo sees red|
|Italy 1 United States 0: Politano snatches late winner for Mancini´s men|
|Scotland 3 Israel 2: Forrest hat-trick seals Nations League promotion|
|Brazil 1 Cameroon 0: Richarlison fills Neymar´s boots as skipper suffers injury|
|France & PSG star Mbappe suffers shoulder injury|
|Albania 1 Wales 0: Gunter´s night spoiled by Balaj|
|Leeds and Manchester United to meet in friendly|
|Outspoken Smith leaves Cavaliers|
|PSG star Neymar injured for Brazil|
|Juventus midfielder Can back in training after surgery|
|Rams-Chiefs rollercoaster was the NFL´s modern-day masterpiece|
|Ronaldo an AC Milan target in 2017, confirms Fassone|
|Farah could get back on track at Tokyo Olympics|