The final section of the Aberdeen bypass is not expected to open until January.
It had been hoped that the 4.5-mile stretch between Parkhill and Craibstone would be ready before Christmas.
Contractor Aberdeen Roads Limited (ARL) this week informed Transport Scotland it will not meet the deadline it set at the Scottish Parliament’s rural economy and connectivity committee earlier this month.
Technical issues during the construction of the Don crossing have held up the opening of the last section.
Transport Secretary Michael Matheson said: “I have consistently urged caution and realism about ARL’s ambitious timescales. Unfortunately, as disappointing as this news is, it comes as no surprise to me it has been unable to achieve this.
“We have been here before with ARL. My officials and I will continue to work constructively and offer every assistance to get the remaining 4.5 miles open as soon as possible.”
Mr Matheson added that although ARL are forecasting the opening for next month, they have been unable to provide a definitive date.
Peter Chapman, a North East Region MSP and member of the rural economy committee, said: “I said before that a pre-Christmas opening for the whole route was very optimistic.
“However, news that a January, 2019, opening cannot be guaranteed will be met with utter dismay.
“This project has been plagued with problems from the start – and it has all happened under the SNP’s watch. It’s not good enough.”
The 20-mile stretch between Craibstone and Stonehaven was opened on December 12.
There has been positive feedback from business owners and road users about journey times.
The project is now expected to cost more than £1 billion.