Massa edged out Lotus rival Kimi Raikkonen and his Ferrari team-mate Fernando Alonso on soft tyres, but technical director Pat Fry says the team is still not convinced about its F138's single-lap speed.
"I think pace-wise, exactly where we are in qualifying, we are still not sure yet," he explained. "It looks like we are a reasonable amount off still, and have a lot of work to do.
"Race pace for the last two races has looked quite encouraging. We have got some more developments here, so we are trying to close the gap that we think we have got to the leading teams. I suppose we will find out tomorrow."
Massa himself admitted that he was slightly surprised by his strong showing on the timesheets but said that it was an encouraging performance considering how the car looks on long-run pace.
"I was not really happy at the beginning with the medium tyres and we were not even so quick compared to the other cars," he said. "But looking at how much we improved with soft tyres, I think that was very amazing. I didn't expect to improve so much like that.
"When I did the race in Malaysia the pace was very competitive, but for sure the biggest problem is always the qualifying. I think I did a good lap on the soft, and degradation on the soft was not bad.
"I am confident for the weekend, and hopefully we can do everything we did today, [both] tomorrow and Sunday."
With the soft tyre showing signs of extreme degradation, Fry thinks the challenge will be in dealing with the characteristics of that compound.
"I think the medium compound tyre here seems quite reasonable," he said. "This morning it was a normal issue you get, but here the track is quite dirty.
"The left front was giving up quite early on and in the afternoon, compared to the soft, the car balance was a lot better.
"Felipe's long run looked quite reasonable, but everyone is struggling to get the most out of the soft tyre."
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