Rosberg is one of just two team-mates to best Hamilton over the course of a season, having memorably beaten him to the title in 2016 after a bitter duel between the pair.
The German recently revealed he required two hours of time with a psychologist every day to put himself in the right frame of mind to beat Hamilton, who looks on course for a sixth drivers' title this year despite Bottas' improving form.
And Rosberg says Bottas is on the right track, but must continue to work even harder.
"In my case, Lewis is a slightly more naturally talented driver," Rosberg told Ilta Sanomat.
"He's the most talented driver in history together with Ayrton Senna, and so the only way to beat him was to do a tremendous amount of work.
"With Valtteri it's the same. You can see he is working very hard and is very dedicated. It's his big strength.
"Last year he had a hard time, but he's taken big steps this year. It's because of all the small details. Even his beard bringing publicity was important!"
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