Toto Wolff admits the 2021 world championship could be "shorter" than the scheduled 23 races.

With covid still wreaking havoc across the world, the Mercedes boss was asked how much more difficult his task is when it is so unclear how long the calendar will ultimately be.

Although Qatar is now expected to be named as a substitute race following cancellation of the Japanese GP, Melbourne's replacement is still unclear and there are concerns about other races in the last part of the season.

"(Charles) Darwin said that not it is not the strongest who survives, but the fittest," Wolff, whose Mercedes outfit is locked in an intense championship battle with Red Bull, told La Gazzetta dello Sport.

"We have to do the same and give our best in every race, because the championship could be shorter."

Amid that intense title battle, Wolff is reportedly still deciding which driver should be Lewis Hamilton's teammate next year - Valtteri Bottas or George Russell.

One fear is that telling Bottas his services will no longer be needed could leave the Finn demoralised just when Mercedes needs him at his best.

"As long as we are transparent with Valtteri and George, we will be able to handle the situation," Wolff insisted.

"The hardest thing for a driver is to not know whether or not he will have a seat. We will decide very quickly.

"But the announcement will depend on the circumstances."

As for the Mercedes-Red Bull title battle, Wolff believes Hamilton has a good enough car to keep his championship lead.

"At the moment we are not inferior to Red Bull, while we clearly were at the beginning of the season," he said.

"In recent months we have made some really excellent developments."

When asked about Red Bull's strong 2021 season, he added: "For me it was clear that Honda would be strong this year. They want to leave F1 with a world championship in their pocket.

"They have climbed Everest since returning to Formula 1 in 2015, so if I wasn't in charge at Mercedes, I would wish them success," Wolff smiled.

Finally, the Austrian said that despite the intensity of the battle, he wants the animosity between the two camps to be confined to the race track.

"I have told Christian (Horner) that the only place we want to battle is on the track, in line with our history and tradition," he told Autosprint.

"I repeat - it is a war, but only on the track."
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