Williams says it remains undecided about when its definitive 2016 nose will be run for the first time.
The outfit launched its new Mercedes-powered car with a 2015-specification nose design earlier this month and stuck with it through the first Barcelona test.
However, it is understood that a tweaked concept is being readied for the start of the season - and will likely to appear at some point during next week's Barcelona test.
When asked by Motorsport.com about when the new nose would appear, Williams technical chief Pat Symonds said: “I am not completely certain yet….but this [nose] isn't it.”
Symonds said that the compact pre-season schedule had forced teams into having a different approach to testing, with last week's test more about reliability and next week's about performance.
“I think we are going to see things a bit different this year,” he said. “Not only are we down to eight days of testing but of course, the tests and first race date moved forward once we had already started the project.
“The project of building an F1 car, it is difficult to determine exactly when it starts, but certainly in the early part of the summer, you are into some quite detailed laying out because project plans are established and everything.
“We don't put much slack into the project plans, so to move everything forward a couple of weeks was tough.
“Traditionally when you have had your 12 days of testing, you go through your stuff and the last couple of days you bring your Melbourne package there.
"You spend a couple of days working there and more or less that is what you have at the first race. I don't think we will see so much of that this year," he adds.
"I think we will see new parts introduced in Melbourne on some of the cars, and we will see less of that last minute introduction of bits.”
Although Williams avoided headline grabbing times last week, Symonds says he is upbeat about the performance of the car.
When asked if it was a step forward on its 2015 challenger, he said: “That is where our concentration has been, and the drivers and the data tend to suggest that we have picked up there.
“Now it is down to what the other guys have done as well.”