2015 MotoGP title runner-up Valentino Rossi believes Yamaha are playing catch-up following the change to Michelin tyres.

With Rossi and team-mate Jorge Lorenzo embroiled in a close championship fight during the second half of the season, Yamaha didn't conduct as many Michelin tests as some of its rivals.

At the close of this week's Valencia test, in which the top Yamaha of Lorenzo was fifth and Rossi seventh, the Italian said:

"For me we need to continue to work because it looks like with the Michelin we are a bit more in trouble. Especially in corner entry and weight distribution. For sure, this is just the first step. But it is not so bad because anyway we improved one-second from yesterday, so we have just to continue to work.

"Today we improved very much the feeling with the tyres, especially the front. This made me quite optimistic. It means that if we work and make some more kilometres we can fix the problems. For sure we have lot to do because the Yamaha uses quite a lot the front tyre, so it needs the right balance."

Rossi, who set a best lap time 0.438s behind Honda pace setter Marc Marquez, also felt progress had been made with development of the single ECU system.

"About electronic from yesterday to today already the situation improved a lot. It is still not at the same level [as this year's factory software] for sure, but it looks like we can improve I think quite quickly.

"Engine brake and especially acceleration, anti-wheelie, traction control. Everything is a bit worse, but we expect. So is normal."

Shortly after seeing a tenth world title snatched way in Sunday's final round, Rossi said his 'motivation to try again' would be one of the most important factors for next season.

Crash.net asked Rossi how he felt after this test.

"Sincerely, yeah, was quite difficult," Rossi replied. "And is still quite difficult. But today is already a little bit better. So it will be important this winter to try to recover enough power, be relaxed and especially recover enough motivation to come back at the top."

It is not clear when Rossi will be back on track, with Yamaha yet to decide if they will join their rivals in holding a private test at the end of this month.

"Yamaha haven't decided. We don't know if we go or don't go. I don't think that one test at the end of November change everything in the championship! But if Yamaha decide to go we are ready."