Already without his usual crew chief Jerry Burgess, Valentino Rossi's home Italian Grand Prix hopes suffered a further set-back when the MotoGP superstar suffered technical problems with both his Ducatis in opening practice.

Left just 13th fastest, after completing 13 laps, Rossi's hopes of making up for lost time during the Friday afternoon session were then thwarted by the weather, with spots of rain leaving the track too slippery for slicks until the final five minutes.

Needing all the track time he could get, Rossi recorded six laps on the new GP11.1 motorcycle - introduced last weekend at Assen - before the chequered flag was waved.

"It's almost as if we didn't have practice today," said Rossi, who concluded Friday 1.793sec behind pace setting countryman Marco Simoncelli. "This morning we only had one complete [run], which went pretty well. Then we had problems with both of the bikes, and I was left with the time that I did on my fourth lap.

"They were really just minor problems, but the fact is that we didn't ride anymore after the early minutes: on the first bike, a wire touched a hot part and the bike stopped. On the other bike, there was a separate electrical problem, and the result was the same.

"The afternoon session was halfway between wet and dry, so it was useless. Only in the final minutes were we able to do three laps to check some changes we had made, and the results seemed interesting.

"We hope we can try them more thoroughly tomorrow to see how competitive we are in normal conditions. Having tested the GP12 here gives us a starting point, but we still have to adapt the 800's setup, as it requires different lines in order to maintain corner speed.

"Tomorrow we'll continue to test, and we hope to get close to the others."

Rossi - winner at Mugello from 2002-2008 - has taken one podium so far this season. The seven time MotoGP champion broke his leg during practice for last year's Mugello round.

Team-mate Nicky Hayden was the top Ducati rider on Friday, in eighth place, as he continued working with the step 2 frame for the original GP11.

"We were pretty strong in our first run this morning. We didn't improve much from there, but I used the same hard tyre the whole session, and it worked well here on both sides," said Hayden. "We made a couple little changes with the bike that felt like they were in a good direction.

"I did my fastest lap on the step 1 chassis, but the data showed that the step 2 had some pluses.

"This afternoon was wet one minute and dry the next. It looked like guys were destroying their wet tyres quick, and there was no point in putting on engine mileage and taking risks. We just went out to check a power setting on a practice start. We'll see what tomorrow brings."