Red Bull chief technical officer Adrian Newey fears that the RB9 could be late, after the team had to focus heavily on developing the RB8 late into the 2012 season.
Sebastian Vettel pipped Fernando Alonso to the 2012 crown, with Newey believing Red Bull's efforts on 2012 could lead to a late start in 2013.
"We were introducing developments to the car right up to the penultimate race," Newey told Autosport.
"That has made it difficult to introduce all of those and simultaneously develop the next car. If I'm honest, this has compromised the timescales of the new car more than we would have liked."
Newey nevertheless agrees with Red Bull's decision to focus on Vettel's push for a third crown.
"It was the right trade at the time, because we managed to get the job done but it means a busy winter trying to catch up again."
The first test of 2013 takes place in Jerez, Spain from February 5th - 8th. Red Bull will announce next week whether the RB9 will be unveiled in time for that test.