Just one week after qualifying in fourth place for his Petronas Yamaha debut, Valentino Rossi will start a MotoGP worst of 21st on the grid for the second of the Qatar rounds.

The Italian began the weekend seeking answers to rear tyre 'overstressing' problems that saw him drop to twelfth place in last Sunday's race.

But the changes made seem to have backfired badly, with Rossi not only in 'a lot of trouble' for race pace but having now also lost his one-lap speed.

Rossi, who had set a 1m 53.114s for fourth place last Saturday, couldn't do better than a 1m 54.881s today.

That left the nine-time world champion quicker than only Aprilia rookie Lorenzo Savadori in Qualifying 1 and 0.950s behind Joan Mir, who progressed to Q2 alongside Miguel Oliveira

The eventual pole time by Jorge Martin was 0.4s slower than fellow Ducati rider Francesco Bagnaia the week before.

"A very difficult day, because I was never strong," Rossi said afterwards. "We tried to improve the feeling with the rear tyre but I suffer very much. I have a lack of grip in acceleration and also, after some laps, I suffer a lot and my pace is not good.

"Also in the qualifying with the new tyre I never had the feel to be fast enough. Last week I was good with the new tyres, we tried to improve the tyre life this weekend but unfortunately I'm not fast enough. It will be difficult. I have to start behind. We have to understand, try something else and we will see."

Rossi's previous lowest qualifying was 18th on the grid while riding injured at Assen in 2006, although he felt his performances during the Ducati years (low of 16th at the 2011 German Grand Prix) were worse.

"For me it’s not my worst qualifying. I think I did worse with the Ducati!" he said, who had been ninth fastest and only 0.654s from the top during the hot and dusty afternoon FP3 session, before sinking to 21st in final practice and then repeating the place in Qualifying 1.

"I have a lot of problems with the [soft] rear tyre but in FP3 with the hard tyres there was a lot of wind and sand on the track, very different conditions and my lap time was but similar (to the other riders).

"But when I put the soft, for some reason I stress too much the rear and after I don’t push because I have also a lot of vibration. Looks like the tyre became too hot and I’m not fast enough."

As Rossi knows, the problem is that all riders raced with soft tyres front and rear last Sunday and are predicted to do so again tomorrow.

"Qatar is always like this. In the last years, you try lots of different tyre combinations but in the end for the race everybody is soft-soft. But the tyre is the same for everybody, so if the other guys are able to use these [soft] tyres we have to. It’s not a question of tyres, I think."

And what now for the race?

"For tomorrow it will be difficult because I start behind, but especially I’m in a lot of trouble with pace, I’m not fast enough. So I need to try and stay with a group of guys in front.

"Last week more-or-less everybody was in a line. There is not a big difference in the group. I will try to stay with them and try to see."

Team-mate Franco Morbidelli qualified in tenth place with the other Factory-spec Yamahas of Maverick Vinales and Fabio Quartararo starting third and fifth.