MotoGP World Championship leader Casey Stoner struggled with pain in his neck during Friday's opening practice session for the Italian Grand Prix at Mugello.

The Repsol Honda rider suffered a nasty highside exactly one week earlier at Assen and, although able to ride to second in the Dutch race, feels there is a 'deeper problem' with his neck.

"This morning we had a pretty tough session, my injuries from Assen aren't completely healed and it seems there is a slightly deeper problem with my neck," said Stoner.

"On the main straights the wind was knocking my head around quite a lot and we struggled with this and weren't able to get enough time on track to find something decent with set up or complete as many laps as I would have liked to."

Despite the discomfort, Stoner beat the previous lap record on lap nine and remained on top of the session until fellow HRC rider Marco Simoncelli dipped 0.040sec under on his final lap.

With light rain spoiling the afternoon session, when the likes of Stoner and Simoncelli stayed in the pits, the morning times proved the best of the day.

"In general the bike worked very well straight out of the box so I'm very grateful for this and cannot complain too much," said Stoner. "There are a few things we would like to improve with how the bike turns, but we didn't get any time on track this afternoon to try anything.

"At the beginning of FP2 it wasn't wet enough for wet tyres, we would have destroyed them, then when it finally was dry there wasn't enough time out there to do a lap or to get any information so it's better we wait until tomorrow and continue from there".

Stoner starts Sunday's race with a 28-point lead over Jorge Lorenzo. The Factory Yamaha rider was fourth fastest on Friday.