After storming to his fourth victory of the season last time out at Estoril, MotoGP title contender Jorge Lorenzo struggled with physical and technical problems on his way to a lowly sixth in Friday practice for the Australian Grand Prix.

First or second in the last three races - when he has scored almost twice as many points as team-mate and title leader Valentino Rossi - Lorenzo was feeling unwell even before he took to the track, then battled grip problems.

The young Spaniard spent most of the session in fifth, before a lowside at the Hairpin in the closing minutes saw him finish the hour in sixth place and one-second behind fastest man Rossi.

"I just couldn't go fast today," admitted Lorenzo. "I wasn't feeling too good - I think that I ate something last night which didn't agree with me and I felt very weak, which made it very hard to ride the bike.

"We had some spin and not enough grip or confidence and there were two times where I nearly crashed before I actually did," he revealed. "Luckily I didn't hurt myself at all and now I will just try to get a good night's sleep and then hopefully I will be much better tomorrow."

Lorenzo's team manager Daniele Romagnoli hopes both bike and rider will be in better shape on Saturday.

"Today we didn't quite make the good start that we've maybe become used to lately, plus Jorge wasn't feeling very well; he was quite weak which made his job much harder," he stated. "The main problem is on the rear, we don't have enough grip on the entry to the corner or under acceleration and at this track these areas are particularly important.

"Unfortunately towards the end of the session Jorge slid off at turn four when trying some improvements. He was okay but now we need to work hard to analyse all the information that we have in order to be in better shape for tomorrow, when we hope that he will be feeling better too."

Lorenzo starts the final three rounds 18 points behind Rossi.