Jorge Lorenzo believes Honda has been handed a definitive advantage over Yamaha as a result of Bridgestone's altered 2014 MotoGP tyre compounds.
The Spaniard has grown increasingly despondent about Yamaha's ability to adapt to the new rubber, and in particular the stiffer sidewalls that reduce edge grip.
Having first spoken of his fears on Wednesday, he is now convinced Honda will have a clear lead on Yamaha over the season as a result of the tyres.
"This tyre is much worse for Yamaha and better for Honda," he said after the final day of Sepang testing.
"We found a better solution today to improve our situation [but] at this track, with this Tarmac that is very slippery, it's impossible for us to be competitive.
"We tried a simulation today and it was worse and worse every lap.
"In the edge there is a problem with no grip but also when you pick up the bike it spins.
"You can improve the feeling a little to get more grip but when the tyre starts to drop the problems get worse and worse.
"Our bike is at a similar level to the competitors, but with the tyre we have problems."
Yamaha team manager Massimo Meregalli believes the issues are exacerbated by Lorenzo's riding style.
While Lorenzo ended the final day seventh overall, team-mate Valentino Rossi was tied for top spot with Honda's Dani Pedrosa.
"It looks like the new tyre doesn't work very well on our bike, especially at this track," Meregalli said.
"At the end Valentino was able to make the fastest lap of the day.
"Jorge continued to have some difficulties, especially because of his riding style.
"We made some improvements but we are not satisfied 100 per cent and we have to improve over race distance."
Rossi meanwhile acknowledged the team "still has some problems" with the tyres, particularly over long distances, but said it had also "made a good step from the first test".