Williams will hold fire on running its definitive 2016 nose for now, with most of its final update package set to appear only at the Australian Grand Prix.
The team has run with its 2015 nose up until now, with technical chief Pat Symonds saying last week that the outfit was unsure on when it would switch to its 2016 specification.
However, with only one day of testing remaining, chief test engineer Rod Nelson has made it clear that it will not be making an appearance at Barcelona this week.
When asked when the new nose would debut, Nelson said: "You will have to wait and see, but it won't be here."
Williams has worked it way through its reliability check list and has begun more performance work this week, switching to qualifying simulations in the slower afternoon sessions.
Nevertheless, Massa ended up with the second fastest time on Thursday on soft tyres - having had his best lap on ultra softs thwarted by traffic.
Nelson said the times being delivered were encouraging but it was hard to know where Williams stacked up against Ferrari.
"We have got some more bits to bring to the car and I am sure they have as well. So operationally we have to be as efficient as we can be and I won't say hopefully they will trip up, but we will do the best job we can.
"It is close – but the Mercedes are gone. We would like to be second up if we could."
Massa hailed his day with Williams as the best outing he had had in winter testing so far.
"It was quite good. In fact, I think it is the best day we had up until now," he said. "We didn't have an amazing week last week I would say, but this week is going very well.
"It was quite good for Valtteri [Bottas] and today was a very good for me to understand the car.
"That is the main important thing because I managed to understand the car in the best way compared to last week, and changing the set-up, and the behaviour of the car."
But he has admitted that winter testing has not delivered any clear answers about where Williams stacks up right now.
"Where we are is difficult to say but I think we can be competitive," he said. "We know Mercedes is in front, maybe Ferrari is there, but I think there can be many different teams behind.
"I hope we can be there in a big fight, but we will know in the first race anyway."