Valentino Rossi concluded Friday's free practice at Sepang in Malaysia one second down on team-mate and MotoGP title rival Jorge Lorenzo but remains confident of closing the deficit tomorrow.

The Movistar Yamaha rider had been fourth fastest in FP1 but dropped down to eighth in the afternoon after encountering handling problems when he switched to the medium compound Bridgestone for a time attack in the final eight minutes.

Rossi, who holds a lead of 11 points over Lorenzo with two rounds remaining, pulled into the pits and changed to his second bike, but only completed an out lap before the session expired and was unable to ascertain if the medium tyre was the cause of the vibration problems he experienced or if the issue lay with his YZR-M1.

The 36-year-old lapped in 2m 01.305s but Rossi, who has caused a stir ahead of the penultimate race of the season at Sepang by claiming Repsol Honda's Marc Marquez had helped Lorenzo's title cause at Phillip Island, is confident of reducing the advantage to Lorenzo and Repsol pair Dani Pedrosa and Marquez on Saturday.

"The day I think was not so bad, this morning I was already quite fast and the most important thing is we have a good base setting from the beginning to work from Friday morning," Rossi said.

"Also for the afternoon I am quite happy with my pace because we decided to work a little bit with the hard tyre for understand if this can be an option for the race of Sunday, both front and rear.

"We had a set of medium tyres, which are a little bit faster, for the end of the session but unfortunately we didn't finish our work and when I started at the end for the last three or four laps with the medium tyre I had a bad feeling with the bike and with the tyre with vibration and I decided to stop.

"I tried to do a minimum of another lap with the other bike to try to understand for tomorrow morning if the problem comes from the tyres or from the bike. Unfortunately it was too late and I take the flag and in the end I wasted the last ten minutes," he explained.

"I'm not happy because it remains a question mark of our potential and I am more behind about the position for sure but I think if I am able to do two laps with the medium tyre, I can improve my lap time for sure."

Rossi, bidding for a tenth world crown and a seventh premier class title, was happy with his pace in the morning and has emphasised the need to get to the bottom of the problem in FP3 and set a fast lap to guarantee straight passage to Q2.

"It is also true that Jorge was very fast but I think that we are not so far," he said.

"We have to wait until tomorrow because if the problem is coming from the tyre we have a problem because the quantity of the tyre is very tight, so we need to wait until the morning to understand and after decide what to do because tomorrow morning will be very important to make a good lap time and a good time attack because we have to stay in the top 10.

"Apart from this, the setting is not so bad and my pace was quite good at the beginning of the practice and it was very similar to the two Hondas, to Jorge, so the pace and the feel with the bike is quite good."

The Doctor reasoned that track conditions at Sepang are comparable to those experienced during the pre-season tests, although the searing temperatures in the afternoon are understandably having an impact on grip levels.

"This morning I expected more dirt [on the track] but I think it is bad conditions with the fog like this but don't have any problems on the track. The level of grip is very low, so I think this is very difficult, so I think it is more or less similar [track conditions compared to winter tests]," he said.

"The lap times are already quite fast so I think the conditions today are more comparable to the tests but during the season we modified the setting of the bike compared to February and also the way to ride - this is normal.

"But in the afternoon it is worse because when the asphalt goes to 50 degrees it is normal that the grip is less."