Valentino Rossi began his quest for a tenth 2008 victory in the Valencia season finale by setting the fourth fastest time during two wet free practice sessions, the second of which saw the Italian slide off his championship winning Fiat Yamaha.

This morning's session was run in very heavy rain and cool temperatures, and Rossi completed just eight laps of the 4km circuit, leaving him in 13th position.

The afternoon saw the rain ease off and the Italian was able make more headway with his wet-weather set-up, completing 21 laps and finishing the session fourth fastest.

Rossi was unhurt when the rear of his M1 spun around on entry to the last corner with 18 minutes to go, sending him sliding into the gravel. After failing to bump start his fallen M1, Rossi later returned to the track on his second bike.

"Today was a difficult day because this track is quite bad when it's wet and cold like this - the asphalt really doesn't give enough grip," said Rossi, who lost the world championship at Valencia in 2006 and was denied second in the 2007 championship when his bike broke down at last year's event.

"This morning I went out just when it started to get really heavy and so I wasn't able to do any good laps, but this afternoon was better.

"In fact I felt good and I was quite fast with the Bridgestone wet tyres, so I think we have good potential if the conditions are like this again.

"Unfortunately I had a small crash at the last corner when I made a mistake and lost the rear, but I wasn't hurt at all and I was able to go back out with a slightly harder tyre and continue to work," he confirmed. "Anyway, we were fourth finally and I am quite happy although we can be faster. Now we have to wait and see the weather for tomorrow."

"Things weren't so bad and Valentino was up there with the fastest riders, but we definitely have a bit more work to do," added team manager Davide Brivio. "He had a small crash when he lost rear grip at the last corner and slid off, but it was very slow and he wasn't hurt. It seems that it's likely that this weather is going to continue, unfortunately, so now we need to put together all the information we gathered today and continue to improve things tomorrow."

Rossi's team-mate Jorge Lorenzo had a promising opening day at his home race, finishing third in both sessions, whilst Repsol Honda's Nicky Hayden topped the time sheets in both the morning and afternoon.

"It's a pity to be coming to Spain in the rain but anyway we made a good start today and I am quite happy," said Lorenzo, looking to wrap up the 2008 rookie of the year title on Sunday.

"This morning was very wet and it was quite difficult to ride, but this afternoon the conditions were a bit better and I was able to be quite a lot faster and also do some good work on the set-up of my bike. My Michelin tyres are working well in the rain and I think we can make some more progress tomorrow if it's like this again, although of course I hope for sunshine!

"It's nice to be back in Europe but it's very busy for a Spanish rider at Spanish race and I have to have a lot of time for everybody! I have a special livery on my bike, which I like very much; it has the flags of all the countries where I have won and was designed by a member of the public in an Italian competition. It's all of 'Lorenzo's Lands'!"