Felipe Massa is concerned Williams may slip back in Formula 1's pecking order, unless it pushes on developing aerodynamic parts for its car.
Williams looked to have the second fastest car in race trim at the season-opening Australian Grand Prix, but both Massa and team-mate Valtteri Bottas complained of a lack of rear grip from the FW36.
The team has introduced cooling updates for this weekend's Malaysian Grand Prix, but Massa feels Williams needs to push on aerodynamically to avoid slipping behind rival teams.
"You're always concerned that maybe some other teams improve their cars and we will have the same car," said Massa.
"We have the same car more or less compared to Australia. This is a different track, so we need to see how the car behaves here, but we're working 100 per cent in the factory to improve.
"I'm sure when we fix the car will grow and show a better balance. We're missing a bit of rear downforce but we're working on that."
The Brazilian feels Williams started further down the grid than it should have in Melbourne, where a wet qualifying session exposed the FW36's rear grip issues.
He expects the team will be able to fight for top six positions in qualifying in Malaysia, even without a substantially different car to the one he drove in Australia.
"We didn't start in the right position [in Australia]," Massa added. "In normal circumstances we could start in the top five.
"We showed very good performance in the race. The car was competitive. If I didn't have the problem in the first corner I think it was possible to get both cars on the podium.
"I think we have a good car anyway and we can be there fighting. Maybe now until Barcelona you will see many different results, many improvements from other teams, from us as well.
"We will see how it's going to happen race by race."