Valentino Rossi will start his final MotoGP for Ducati from just eleventh on the grid at Valencia on Sunday.
The Italian had problems with the front end, especially in bringing the hard front tyre up to temperature on the right side, and was beaten by top CRT rider Aleix Espargaro.
“Today went pretty badly, and I'm sorry because we really hoped to do well in these last races,” said Rossi, who will make his Yamaha return in Tuesday's test.
“It's also true that Hayden, Barberá and Bautista aren't so far ahead, so tomorrow we'll certainly try to do a good start, to pass some people and make up some positions.
“Unfortunately, today I had some problems with the hard front tyre. I lost the front twice at mid-session because we're not able to get it up to temperature well on the right side.
“The race should be done with the hard, so we'll see what the temperature is tomorrow or if there's bad weather. If it were to rain, we would certainly be more competitive.”
Team-mate Nicky Hayden was the top Ducati rider in seventh place, 1.65s behind pole sitter Dani Pedrosa (Honda) and 0.374s ahead of Rossi.
“It's been strange with the weather this weekend. We had to basically go out in qualifying and spend some time to understand the new grip and also the bike, then try to get a good time.
“The bike was okay, but the front was pushing a lot, especially on corner entry, with the brake still on,” said Hayden. “The new pavement certainly helps the bike feel better, and I thought we could be closer to the guys at the front, but they went really fast today.
“I'm not too thrilled with how it went, but we have a couple of ideas to try in warm-up tomorrow. We'll see.”