The 31-year-old was, after all, in Bottas' seat before he surprisingly retired five days after winning his first world title last November.
"Don't expect an easy ride," Rosberg replied Monday when asked to offer his Finnish successor advice on dealing with Hamilton.
"It's going to be challenging coming into a new team with Lewis having been there for so many years and with the new regulations.
"Lewis is one of the best out there so the level is extremely high.
"But Valterri Bottas is extremely talented and he can achieve great things as well, as long as the team give him a good car."
Hamilton and Rosberg were best friends when they were teenagers, but their relationship cooled during their four years as teammates and rivals with Mercedes.
Rosberg, nevertheless, insisted he would not reveal any secrets to former Williams driver Bottas on how to get the better of Hamilton.
"He has asked if we can have a chat soon and I am happy to do that, of course, but I will stay very, very neutral," he said.
"I won't give away any of Lewis' secrets, for example. I'll just help him in a way to integrate better into the team."
Speaking before Tuesday's Laureus World Sports Awards in Monaco, the world breakthrough of the year nominee said he hoped he and Hamilton could become friends again.
"We've already had some nice relaxed moments," Rosberg said.
"I'm hoping to have a better relationship with him in the future. We were best friends, after all, 15 years ago."