Germany's Auto Motor und Sport now has more details.
It has published detailed photos that depict the supercar, with a camouflaged livery, also featuring a "suspiciously large" air intake on the roof.
The car also had a "giant wing" at the rear.
Correspondent Tobias Gruner said it is obvious the car was not powered by its usual V12 engine, but a "small-volume turbo engine".
And on the livery was a triangular, yellow warning sticker, indicating that complex electric technology lurked beneath -- perhaps the sort of sophisticated energy-recovery systems that will power the team's 2014 F1 car?
"Ferrari will not publicly comment on the test," Gruner said, adding that it is also possible Ferrari was testing in preparation for a potential Le Mans project.
But the heavily-modified LaFerrari also featured a F1 2014-style, single and central exhaust outlet at the rear, while the car "sounded suspiciously like" the audio clips that have been released depicting this year's turbo V6s in development.