Mercedes Motorsport boss Toto Wolff has upped the pressure on Valtteri Bottas for the 2018 Formula 1 season, claiming there is "no excuse" for him not to challenge teammate Lewis Hamilton.

The Finn made a strong start alongside the Briton last year following his late move from Williams but would tail off in the second half as a combination of struggles with car setup and simply being unable to keep up with Hamilton took off some of the shine.

He would hit back strongly in the closing races finishing second in Brazil and winning in Abu Dhabi, however, on just a one-year deal and with names like Daniel Ricciardo and Esteban Ocon being linked to his seat, producing those results more often is now a requirement from the Mercedes hierarchy.

"That's what he has to do," Wolff told ESPN. "If he can step up and challenge Lewis he has his place among the greatest drivers in F1, if he doesn't he's going to know it and there is no excuse."

The Austrian has a long history with Bottas, having been a part of his management team for much of his career as well as being a shareholder in Williams before switching to Mercedes, therefore, he has confidence the 28-year-old will respond.

"He is a Finn with a strong never-give-up mentality," he said. "Valtteri will improve his weaknesses and continue to work on his strengths. I expect him to come back strong with all the learning he has done during the season.

"I have no doubt we will see a better Valtteri in 2018."

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Earlier this week, controversial former world champion Jacques Villeneuve described Bottas' performance as "embarrassing" and suggested Pascal Wehrlein would have been better, however, Wolff rejected the Canadian's opinion.

“We like working with Valtteri and with Lewis," he insisted. "The two fit well together. They have a good dynamic in the team and see no reason to change it."

Toto has claimed it would be better for Mercedes if there was a little more needle between Bottas and Hamilton, however, he doubts the former GP3 champion would resort to any Nico Rosberg-style mind games. 

"That's not at all Valtteri's style," he believes. "Valtteri wants to do it on the track in the best possible way, he wants is to be benchmarked against a four-time world champion. He's brutally honest with himself."