Bottas became Hamilton’s Mercedes team-mate following Rosberg’s retirement in 2016.
Rosberg says to beat the reigning champion you have to be on your game for every race and he reckons Bottas has what it takes to do that.
“That’s the only way to beat Lewis, it’s to be really 100 per cent with everything, do the perfect season, otherwise there’s no chance,” Rosberg told Sky Sports.
“That’s what Valteri needs to try but I can see a lot of that in Valteri’s approach as well.
“He’s very, very professional, really giving it everything, living for doing great in racing.
“Every day he’s preparing for the first race and everything so ultra-professional.
“I think that’s what he needs to do to try and beat Lewis.”
Bottas finished third in the 2017 drivers standings behind Sebastian Vettel and Lewis Hamilton.
Vettel is expecting a better second season from the Finn this year.
“It was his first season and really it was big, big shoes to jump into in the Mercedes team, they were the best team in the world,” Vettel added.
“It was a big mission for him, not easy and I think taking that in consideration he did really well for a first season.
“He can really build on that now and make further progress.”
The F1 season starts this Sunday with the Australian Grand Prix in Melbourne.