Ferrari's technical director Aldo Costa says the Italian squad are still behind schedule with the development of their Kinetic Energy Recovery System.
KERS will be introduced in F1 at the start of 2009, but the development has been hard for many teams, who had no previous experience of the technology.
Costa admitted he would have preferred to have tested the system on track already, like some of their rivals have done.
When asked what was the biggest challenge for next season, he said: "KERS because it's a technology never tried before, but work has been very intense on aerodynamics too.
"There have been reliability troubles," Costa told Gazzetta dello Sport.
"I can't deny we are running a bit late. Let's say that I would like to have tried our system already."
He added: "We have a lot to do but time is short. Even though we have two weeks more compared to the past, we must follow the collective tests calendar. There's a test in mid January and we can't miss it.
"By fighting for the title we've put a lot of resources on the F2008, and now we find ourselves in the need to quickly make up for it. Most of the components are already in production, while the KERS is on the bench."
Costa also said next year's car will be strikingly different due to the radical new regulations that will come into play.
"The front wing will be striking because it will be as wide as the car's track (the distance between the wheels on the same axle). A lot of them will come off because, since they cover the wheels, it will be easy to lose them in crashes.
"On top of that, the rear wing will be taller and narrower, the bodywork smoother and more sealed off because we won't have the current liberty of opening air vents anymore, and this has forced us to heavily re-design the cooling system."