Eugene Laverty was anything other than pleased at the close of MotoGP qualifying, which produced his best Saturday performance to date, and feels a potential pole position charge was ruined by adjustments to his rear tyre pressure.

The Northern Irishman believes a Michelin technician altered the pressure "in the wrong way" - and against his wishes - ahead of Q2, leaving the rear feeling "like a slick" in worsening wet conditions.

"It was a f**king disaster," was his frustrated conclusion.

Coming off the eighth fastest time in FP4, Laverty comfortably topped Q1, guaranteeing his second trip into Q2 in three races. At that point "everything was perfect". But he soon realised he could not match the lap times of the previous session.

Sitting sixth with the clock running down, Laverty pushed despite the lack of rear grip. Indeed he was fastest through the second split, but a crash came as no surprise. Bettering his best qualifying result in the class by five positions was little consolation to the visibly frustrated 30-year old.

"I was really angry," he said. "The bike had felt perfect in FP4 and Q1. There was a problem with the bike in Q2 and it was a disaster. The rear tyre felt like ice and that's why I was wobbling around a few seconds slower than what I did in Q1.

"On the last lap out of anger I thought, 'What the hell. Just go for it.' It felt like I was going to crash in every corner because the rear tyre felt like a slick.

"For some reason the Michelin technician changed the tyre pressure and it went completely the wrong way. [It was] Against my orders really. It was a disaster. That's why I crashed. The bike as it was on Q1, everything was perfect. Then in Q2 it was a f**king disaster.

"Everywhere, the tyre was not keeping its shape. It was not a wet essentially. Wobbling around at the front doing 2m 20s when in Q1 the last lap after my fastest one I did a 2m 18.8s. Then I couldn't get within a few seconds because there was a problem with the rear tyre.

"I'm really upset with that. He went down with the tyre pressure, which was the wrong way. I'm just so pissed off with it. It was the opposite of what I wanted to do. I thought we had left everything the same. What can I say? A real f**k up."

Asked why he felt the tyre pressure was altered ahead of the final 15-minute MotoGP shootout of the day, Laverty suggested it was done with the worsening conditions in mind.

"I guess it was drier before but then it pissed down with rain. That's why we should have left it the same. I don't want to say too much about it. It's a sixth position and I should be happy with that but with the bike we had in Q1 there was a pole position today. We lost a good shot at it. You don't get so many chances like that. That's why I'm so upset.

"It's frustrating. I hate talking about potential. I'd rather just do it. When it's wet we know that we can really be up there amongst them. It really levels the playing field. I can get in among guys like Rossi and Marquez.

"I can't get near them in the dry. It's pretty cool when it rains, we're consistently there. If it's dry it isn't bad. This morning we struggled a little bit. We'll see what tomorrow brings."

Contradictory weather forecasts for race day circulated on Saturday evening, and Laverty feels that he has some work to do on his dry weather pace.

"Yesterday it was OK but this morning I struggled a lot. We need to try and get back to yesterday's pace.

On tyre choice he added, "It's difficult to say right now because we missed the session where we test that: FP4. I looked at some of the lap times in FP3. It seemed the guys that kept their pace better are the guys that dropped their power. The Aprilias really kept their pace.

"Unfortunately here is very slippery. There isn't much grip and that's when the power goes against you. That's going to really work the tyre. We'll have to look at it tonight. I haven't decided on the [dry] rear tyre yet."