Mercedes team boss Toto Wolff has admitted to being wary of McLaren and Renault looking ahead to the 2018 Formula 1 season.
Wolff's Silver Arrows have been relatively unchallenged since the hybrid-turbo era was introduced in 2014 with four successive constructors' championship titles secured.
British driver Lewis Hamilton has claimed three drivers' championship crowns and his former Mercedes' team-mate Nico Rosberg claimed his maiden world title for the team before opting to retire days later just over 12 months ago.
I am curious to see where McLaren and Renault come out. I wouldn't write anybody off. The rules will stay the same so it could be a very competitive season.Toto Wolff
Ferrari emerged as a real threat in 2017 with Sebastian Vettel finishing second behind Hamilton and ahead of Mercedes' current second driver Valtteri Bottas, while Red Bull were not too far off the pace.
The pair are again expected to challenge in the new year, but Wolff can also see Renault potentially gate-crashing the party, along with McLaren after their switch from Honda to Renault engines.
"We mustn't discount anybody," said Wolff. "Today, as it stands, it looks like Ferrari and Red Bull.
"I am curious to see where McLaren and Renault come out. I wouldn't write anybody off. The rules will stay the same so it could be a very competitive season."
He added on the Formula 1 website: "I guess we will see a fight between Mercedes, Ferrari and Red Bull Racing - and maybe McLaren-Renault will join us in the title fight. That is an exciting outlook for the fans."
Hamilton is 1/500 to retain his F1 title in 2018, Vettel is 50/1 to win, McLaren's Fernando Alonso is available at 4000/1 and Renault's Nico Hulkenberg is priced at 4000/1.
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