Valtteri Bottas needs to push Lewis Hamilton for the Formula One world title in 2019 if he wants to hold onto his seat at Mercedes, according to Toto Wolff.
Bottas enjoyed an impressive first season with the Silver Arrows after replacing Nico Rosberg in 2017, winning three races and finishing on the podium in another 10 grands prix.
The 29-year-old finished 58 points behind Hamilton in the title race, but he struggled to replicate that form last year.
He failed to win a race across the season and only claimed eight podiums as he ended up fifth in the drivers' standings, 161 points adrift of his championship-winning team-mate.
And Wolff has warned the Finn his performances need to improve to ensure his seat does not come under threat.
"Valtteri knows exactly where he needs to be next year," the Mercedes team boss told Autosport.
"He needs to have all the bad luck gone and perform on a level with Lewis. He knows very well that, and he has that in him.
"Lewis improving means Valtteri needs to improve. I've seen that improvement all the time with him, but you are going against a five-time world champion.
"He needs a start where it's right up there with Lewis and all the other drivers for the championship. That is what he needs."
Beating Hamilton is something only Sebastian Vettel has come close to in recent seasons, but Wolff believes Bottas has the ability to challenge the five-time world champion.
"We are seeing the best Lewis that I've seen in the last six years, and there is a reason why he is a five-time world champion," he added.
"Beating a five-time world champion at the peak of his performance is going to be very difficult and Valtteri knows that. But I think that he has it in him.
"He can win - he has proven it [in 2018] on a few occasions, but he had bad luck or was in a position where he could not win.
"If that turns into a positive momentum that is actually driving for the championship, I think that Valtteri can win the championship."
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