MotoGP rookie Marc Marquez retook the world championship lead with his second victory of the year, in Germany on Sunday.

But Marquez could face one of his toughest tests of the season at next weekend's US Grand Prix at Laguna Seca.

The 20-year-old has no prior experience of the unique Californian circuit, since the smaller grand prix classes do not race at the track and there are no MotoGP tests held at the venue.

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So just how difficult will it be for Marquez?

That was the question put to Valentino Rossi, seated alongside Marquez after finishing third in Germany, during the post-race Sachsenring press conference.

"No, no, very easy!" Rossi laughed. "At Laguna... I expect that this f**king b*stard is fast from the beginning!

[More laughter with Marquez]

"Joking aside, Laguna is very difficult. It is a strange track. Something very particular. But I'm sure Marc will be fast. For him one weekend is enough to be competitive."

Cal Crutchlow, second at the Sachsenring, later offered some Laguna Seca 'advice' for Marquez: "The first corner is sixth gear!" he smiled.

Marquez, who has finished on the podium in all but one race this year, now leads the standings by two points from injured Repsol Honda team-mate Dani Pedrosa.