Brazilian Felipe Massa conceded Friday that the Williams team's decision to take an aggressive upgrade package to the Austrian Grand Prix had not worked in opening practice.
The package included a revised front wing, new bargeboards and sidepods.
But Massa, who wound up 11th fastest, four places ahead of his Canadian rookie team-mate Lance Stroll, said they had struggled.
"It's not good, to be honest," he said. "We didn't have a great Friday.
"We're struggling with the balance in the high speed, so there's a lot to try to understand to make the car more competitive for tomorrow.
"So, I really hope we can do it. At least the engineers said it should be OK.
"We took it off in the afternoon just to not damage it – and we had damage in the morning actually! We'll put it back tomorrow, and we should run with the new pieces."
Stroll was also optimistic.
"There are bits and pieces to work on overnight," he said. "For sure we don't look as competitive as in Baku, for example. But that can change."