Valentino Rossi's tyre woes continued at Sepang even if the Yamaha Factory Racing rider climbed the leaderboard into fourth position.

Rossi and team-mate Jorge Lorenzo feel the new Bridgestone tyres have had a bigger adverse impact on the performance of their YZR-M1s compared to their Honda rivals and the MotoGP legend admitted Yamaha were 'in trouble'.

The Italian's best time of 2m 00.605s left him over half-a-second off the pace set by Dani Pedrosa and Rossi was unable to make any progress with the new rubber in Malaysia on the penultimate day of the test.

"Today was not so bad, I am fourth, but I am a little bit worried because with the new tyres we are in trouble," he said.

"The bike has become more difficult to ride and gives us more problems with understeer and not so much grip in acceleration. We tried a lot of different things today but we don't fix the problem.

"The Honda was very fast and it looks like this with tyre our bike suffers most, so we have to try to fix the problem. With the Yamaha we have to try to do the lap time with the corner speed but with this tyre the bike moves and we lose time."

Rossi also expects Marquez to extend Honda's apparent current advantage on the new Bridgestones, leaving Yamaha with an even bigger Mountain to climb at the opening race in Qatar.

"It was a good lap (by Dani Pedrosa) for the second day here - it was very fast. We are also worried because [Marc] Marquez is not here but from what we saw at the first test, Marquez was faster than Pedrosa so we imagine that Marquez will also be faster than this," said Rossi.

"We have no grip on the edge and it's bad because this tyre is good for the Honda and bad for the Yamaha."

Lorenzo refused to speak with reporters at Sepang after ending the day in ninth place, over a second behind Pedrosa.