The two had a fractious relationship when at Mercedes together between 2014 and 2016, and that rivalry was rekindled by Rosberg’s comments earlier this week.
The 32-year-old has joined Sky Sports’ coverage team for the upcoming F1 season and pinpointed Hamilton’s apparent inconsistency throughout a season.
Rosberg explained: “He has these periods where he is just not on it.”
Hamilton won the Drivers’ Championship in both of their first two years together but was bettered by the German in 2016, with Rosberg retiring after winning his one and only title that season at what he called the “pinnacle” of his careeer.
The Briton regained his status as No 1 last season by beating Ferrari’s Sebastian Vettel despite trailing Rosberg’s fellow German by 14 points at the summer break.
But Hamilton believes he has nothing to prove in terms of consistency and claims his form last season – winning nine races to finish 46 points clear at the top – shows as much.
“I think I’ve proved that that’s not the case last year,” he said in a press conference previewing the 2018 Australian Grand Prix.
“Again I think there’s a lot of people that need to get headlines and so maybe that’s one way of saying it.
“But no, the goal this year is to be even more consistent than I was last year.
“I think consistency was the reason I won the world championship last year.”
Hamilton starts the season as the favourite as he looks to claim a fifth career title and match F1 legend Juan Manuel Fangio in the process.