Red Bull chief engineer Adrian Newey admitted that the reigning Formula One Constructors Champions are once again "trying to catch up" with work on its 2013 car after such a close end to last season.
German Sebastian Vettel claimed his third consecutive Driver's Championship at the final race of the season - at Brazil's Interlagos track - after being challenged by Ferrari's Fernando Alonso, and Newey conceded that Red Bull were working on their car until nearly the end of the season.
They continued to update the RB8 car until the United States Grand Prix - the second last race of the calendar - which compromised the development of their RB9 car as a result.
"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."
The highly-regarded technical officer added that it proved to be the right decision to focus on the RB8, although RBR are now facing a race against time to get the RB9 up to scratch.
"If I'm honest, this has compromised the timescales of the new car more than we would have liked. 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."
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