Valentino Rossi says Movistar Yamaha have a lot of work to do to catch Repsol Honda after Tuesday's opening round of testing ahead of the 2016 MotoGP season.
The Italian - who lost the 2015 title to team-mate Jorge Lorenzo on Sunday - was well off the pace in Valencia as he finished eight tenths of a second behind Repsol's Marc Marquez as the teams used their new bikes and began to test Michelin's tyres as they take over from Bridgestone as the sole supplier.
Rossi commented: "It's a big change and it will be interesting, especially the tyre will make a big difference for next year.
"It looks like our competitors are a little ahead, because they've made more kilometres with the Michelin.
"I also tried the new electronics and that, as I expected, was quite a big step because it's like going a little bit into the past."
Champion Lorenzo echoed Rossi's concerns as he was only quick enough to finish fifth fastest.
He said: "We started the test with completely the same bike as the race, just with the Michelin tyres.
"At the beginning it was difficult to get good lap times, but by changing the setting of the bike little by little, we improved the feeling of the front quite a bit. [But] we didn't solve the problem completely."
Marquez, who was unable to beat his early time once aboard the 2016 Repsol Honda, had mixed emotions after the opening day.
"We started on the 2015 bike, then the 2015 bike fitted with the new software," he said.
"That is where we spent the most time and we must still spend a lot of time, because looks like we did like one step back [in time] because it will be difficult to arrive at the same level as before. "