Ducati riders Andrea Dovizioso and Nicky Hayden suggest the revised Desmosedici GP13 is not much of an improvement.
The duo, along with test rider Michele Pirro, carried out a two-day test at Mugello on the 'laboratory' version of the bike in an attempt to gain familiarity and gather data, although their running was curtailed on both days through afternoon showers.
Dovizioso, whose fourth in the French Grand Prix is Ducati's highest finish of the season, clocked in 70 laps during testing and his initial impression is that the new GP13 shows little advancement.
"The improvements aren't huge," he said. "This frame won't make enough difference to reduce the gap, but for me it's still a small improvement. We'll see if we can have it ready for the weekend in Barcelona, or if we'll just use it in the postrace test."
Hayden spent 103 laps on the bike and shared his teammate's disappointment with its lack of progression.
"We didn't achieve the progress we hoped for, which is unfortunate," he said. "At the moment, the lap time is very similar to our current bike. Hopefully these days will help the engineers to learn something."
Pirro will use the lab bike when he rejoins the Pramac team to substitute for Ben Spies again at Barcelona next weekend.