Valtteri was sixth, surviving his own hairy moment in FP2, skating through the gravel at the right-hander Turn 11 before returning to the pits.
"Those were obviously tricky practice sessions," said the Finn. "We had quite limited running because of the rain in the morning. I also had a bit of an off in FP2 that cost us some time, we lost a few laps because of that. And then there was of course the red flag in the end.
"We didn't get all the test items tested today, but I think that is going to be the case with all the teams.
"We're definitely lacking some performance, it seems like Ferrari and Red Bull are very strong. So we have some work to do if we want to be in the front row tomorrow. The car balance itself didn't feel too bad; it's just a question of overall grip.
"The key area we are going to need to focus on tonight will be getting the maximum out of the tyres over one lap."