Valentino Rossi's 2012 MotoGP chances took a blow after set-up problems saw him finish 10th fastest on a "negative" final day of testing in Malaysia.
Seven-time champion Rossi said his Ducati GP12 was dogged by corner entry and riding position issues, despite traction control improvements.
"The only positive is the distance to first is a bit less, but unfortunately our position is a lot worse," he said.
Honda's Casey Stoner led team-mate Dani Pedrosa by 0.175 seconds.
Italian Rossi, in his second season at Ducati, had managed to cut the gap to Stoner by one second, whilst his team-mate Nicky Hayden finished 11th.
"Being just behind the factory Hondas and Yamahas after the first test was positive, but everything we tried here - especially to fix our biggest problems - didn't work," said Rossi.
"We are closer to the top, but now we also have the Monster Yamahas and satellite Hondas in front of us. We are very worried for this reason especially.
"The new electronics worked well, and helped in the straight, but I'm too slow on corner entry and I cannot keep the right corner speed. I also have some movement in acceleration.
"We are not very, very far - but 0.6 seconds in the pace is quite a lot."
The 32-year-old, who had talked about retiring after the 2014 season, added that his biggest difficulty is understeer costing him time in the corners.
But he felt the 1000cc GP12, which features Ducati's first aluminium twin-spar frame, was still an improvement over last year's troubled carbon fibre then part-aluminium 800cc machine, which managed only one podium.
Italian Andrea Dovizioso continued to make big strides on the Yamaha and was three tenths from Stoner on his Tech 3 machine, with Yamaha's 2010 World Champion Jorge Lorenzo fourth quickest.
A further test is scheduled for Jerez in Spain (23-25 March), ahead of the first race of the 2012 season in Qatar on 8 April.