Christian Horner believes the remaining tracks in this year's Formula 1 season will not allow Mercedes or Red Bull to run away with the championship.
There are seven events remaining in 2021, with Lewis Hamilton leading the Drivers' Championship by two points from Max Verstappen.
The last two races in Sochi and at Monza have suited the characteristics of Mercedes' W12 and Horner doubts the defending champions will have a big margin at any of the remaining circuits.
"I don't think there's any circuits that stand out as strongly as Russia and Monza," Horner told RacingNews365.com and other select members of the press.
"For sure, Mercedes will be strong. They won in Turkey last year, they will be strong there. But then we start getting to Austin, we should be there or thereabouts. Brazil and Mexico, we've always been strong.
"We don't know anything about Qatar, we don't know anything about Jeddah and then [it's] Abu Dhabi.
"You can say it's 50/50 in what is left on the table, with which favours slightly one team more than the other."
Hamilton's win in Sochi was the first time he won a race – when he and Verstappen have taken the chequered flag – since the Spanish Grand Prix in May.
Horner believes the title race will go down to the wire at the newly-reprofiled Yas Marina Circuit at the Abu Dhabi GP on 12 December.
"This is going to go all the way to Abu Dhabi," said Horner. "I've got absolutely no doubt about that.
"I think that it's going to be a phenomenal competition."
F1 Podcast: Are Mercedes and Hamilton hiding reliability problems in F1 title race?
Lewis Hamilton claimed his 100th Grand Prix win to move into the championship lead, but it's Red Bull and Max Verstappen who will be happiest after the Russian Grand Prix.