Rossi is also unhappy with security at Laguna Seca

The United States is hosting a Grand Prix for the first time in 11 years but Rossi is unhappy with the track.

"This track is pretty dangerous in many points, but there are some places where it's very, very dangerous," he said.

American Nicky Hayden delighted the crowd by leading the practice times, ahead of Australian Troy Bayliss.

Hayden's team-mate Max Biaggi was third fastest.

Series leader Rossi, making his US debut, was over one and a half seconds slower than Hayden in ninth.

The Italian said: "The level of security is not very good, it's not as good as the other tracks we race at.

"If we don't make some changes to this track for the future we might not be able to race here again."

Along with Rossi, Toni Elias, Marco Melandri, Gibernau and Shinya Nakano are all making their US debuts.

Italian Melandri became the first victim of the dreaded Corkscrew corner when he fell from his Movistar Honda in the morning session.

He injured his right leg but was able to continue in the afternoon.

Britain's Shane Byrne, still looking his first points of the campaign on his Roberts Proton, was 19th on his Laguna debut, while James Ellison was one place back.