Rosberg must win in Monaco, Montreal - Prost

May 23 (GMM) Monaco is a crucial race for Nico Rosberg.

That is the claim of F1 legend Alain Prost, as he considered whether the German can take on Mercedes teammate Lewis Hamilton for the 2015 title.

"Let's see what happens here in Monaco," the quadruple world champion told Der Tagesspiegel newspaper.

Rosberg broke Hamilton's run of poles and wins in Barcelona, but Frenchman Prost said his real challenge will be on the streets of the Principality.

"Nico has never won two races in a row," he noted.

"Only if he wins now in Monaco and then in Montreal will Lewis be disturbed. I think this race will largely determine the course of the rest of the season for Rosberg," added Prost, 60.

Rosberg has won the past two Monaco grands prix, while Hamilton has been openly admitting that his eight races on the fabled streets have not been among his best.

But Prost said: "The last time I saw some weakness in Hamilton was when he drove for McLaren.

"Now he is very strong, and if nothing changes, he will remain strong. Nico needs to look for a different approach, whilst remaining himself."