Ferrrari number one driver Fernando Alonso has warned that they will need to evaluate today's results from practice with 'a lot of care'.

Alonso was quickest in both sessions on Friday ahead of this Sunday's F1 2010 Belgian Grand Prix, and while it was a very good start for the Spaniard - and the Scuderia, he remains cautious.

Indeed despite saying it was 'definitely a positive day', he added that the weather could play a 'key role' this weekend in deciding the outcome of Sunday's race, the 13th round on the schedule.

"The impression one gets on Friday does not always get confirmed on Saturday and Sunday, therefore we have to evaluate today's results with a lot of care," Alonso confirmed. "The times count for little, or nothing at all, because when the track changes so quickly, times can improve or get worse by two or three seconds depending on the moment when you are out on the circuit.

"Having said that, it has definitely been a positive day and the car seems to respond well in all track conditions that we encountered today. I think though that the weather will play a key part this weekend, both tomorrow and on Sunday: anything could happen.

"We tried to test all the new components we have here. If the track was to be dry tomorrow, then we must try and improve our set-up, because obviously it is not yet at its best for these conditions, given that we only had a few minutes to test on slick tyres. In fact, I felt the car was a bit nervous, while in the wet it was easier to drive.

"When thinking about going for pole position, first of all we will have to see what the weather is doing: for sure if it was to rain we will go out immediately because you always learn from bad experiences."

Team-mate Felipe Massa meanwhile was only eleventh in the wet opening session this morning, before improving in the mixed conditions of FP2 and setting the fifth best time.

"I am very happy to be back racing at this track, having been forced to miss it last year: I love driving here. From what we could understand on a day like this, the car seems reasonably competitive and that was particularly true on the rain tyres," Massa said.

"However, it is only Friday, so we will have to wait to see how the Red Bulls go, given that so far they have proved to be the quickest cars, as demonstrated in qualifying. We had so many things to test today, which explains a few slow laps this afternoon.

"On the intermediate tyres I immediately had good grip, but even on slicks the situation was not that bad. On the final lap, the only one on the soft tyres, I made a mistake, but the car felt good: obviously there is room for improvement and that is what we will try and achieve tomorrow."