The Briton was fastest in the second session, but told his team that he was not happy with the car, having struggled with a suspension problem in the first session.
The 2008 world champion, who has won the last two races, told Sky Sports News: "[I've not learnt] much. It's not been the easiest of days. This evening we have got to do some work to figure out where we are.
"Obviously we are not that bad, but you always want to be better and we will work hard tonight to find some improvements on set-up."
Qualifying for Sunday's race takes place tomorrow morning.