Toto Wolff believes Mercedes face a big challenge to defend their world titles after their rivals changed driver line-ups for the upcoming 2021 Formula 1 season.
The Austrian is weary of the threat from Red Bull with F1's newest Grand Prix winner Sergio Perez joining the team alongside Max Verstappen.
"This is a very strong combination," Wolff told Speedweek. Red Bull Racing actually had the fastest car at the end of last year, so the team 2021 is in the favourite circle, especially in the constructors' championship, with drivers of this calibre.
"I see Red Bull Racing as a double challenge, i.e. in both World Championship categories, drivers and brands."
Wolff finds Aston Martin's chances particularly interesting given the strength of the car at some events last year. Sebastian Vettel joins the team which Wolff finds an intriguing prospect.
"If you bear the name of an automobile manufacturer with this great tradition, you have to have demands for driving at the very top," said Wolff. "This is also an appreciation for Formula 1 by a great brand.
"For Sebastian Vettel and his stablemate Lance Stroll, this will be a first reality check. It will also be fascinating for me to watch Aston Martin."
The Mercedes team principal thinks McLaren can be a surprise but the young duo of Charles Leclerc and Carlos Sainz at Ferrari could be the biggest movers after the Italian squad finished sixth in the constructors' championship in 2020 - their worst result for 40 years.
"It will be exciting to see if Sainz can beat Leclerc. Ferrari will be stronger than 2020, the Scuderia just needs it. It also suffered from a weak chassis in the previous year. I assume that bugs have been corrected," Wolff added.
Wolff was asked about Fernando Alonso's chances in 2021 as he returns to the sport after a two year absence. Alonso is back in training after a cycling accident earlier this month and his comeback is something that Wolff is looking forward to.
"The interesting thing here is the comparison of the very boys, this fast-yet-teenager, with the 40-year-olds," said Wolff. "Fernando is one of the most talented drivers and one of the strongest fighters who will be competitive. Alonso will want to show that he can still do it, I'm sure."