F1's worst-kept secret was finally confirmed ahead of this weekend's Italian Grand Prix, with Russell's switch from Williams to the factory team revealed a day after Valtteri Bottas had announced his move to Alfa Romeo.
Speaking on Sky Sports F1 about the challenge Russell faces against the seven-time champion, Rosberg said: "Well, the positive is he has nothing to lose.
"You have nothing to lose and everything to gain because you are up against the best of all time.
"No one expects you to destroy him but if you manage to, you will be the absolute biggest hero of all time.
"That is what makes it so difficult for Lewis because he has this young gun coming in having never won anything.
"For Lewis, he can only lose actually. He is the greatest and suddenly this young guy starts to beat him. That is a really uncomfortable situation to be in."
Rosberg questions "first wheel-to-wheel battle"
Bottas has been unable to achieve parity with Hamilton across his five seasons with the team despite regularly threatening with a stellar qualifying pace.
Rosberg believes the biggest difficulty Russell will face will be the first time the pair tussle on track.
"The challenge for George, in the first wheel-to-wheel battle, does he then yield or does he stick in there?" questioned Rosberg.
"It is so difficult because if he sticks in there and it is entirely his fault, that would be a disastrous start to his time at Mercedes.
"If he sticks it in there and it is not his fault and it is more Lewis' fault, it would be a giant boost for the confidence. It is such a difficult one to manage.
"Valtteri has been too conservative over five years now, so he has got it a bit wrong. There are other examples of being too aggressive. It is such a fine line."
What do you think?
this is nonsense of course!!!, are we really to believe that Mercedes with a 7 time champion are willing to give equal standing to a relative newcomer, to risk tarnishing Hamilton's achievements(and their own) by beating him? NO Russell will be No 2 as long as Hamilton is there-I have no doubt it is in both contracts...
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