A source close to the project said the next monthly report by George Reid, the parliament's presiding officer, would list new difficulties.
The source said: "The report is likely to show further slippages.
We are looking well into next year [for completion], probably July for certain parts."
Reid is due to present his update to MSPs in the last week of this month. If it does predict further delays, it is certain to intensify the political furore surrounding the parliament: the cost of the project has risen nearly tenfold since it was first announced in 1997 and has become a cause célèbre north of the border.
Building understands that two parts of the project, the MSPs' office accommodation and Queensberry House, should be completed by the end of this year.
Delays are likely to hit the other parts of the scheme, including the debating chamber and external works. A source said: "There is substantial work outstanding."
A Scottish parliament statement did not give a final completion date, but said that some elements would be completed by December.
Building revealed in June that the team had been faced with 545 instructions from architects in May alone, despite a design freeze imposed in April. A source said: "There have been further variations in the past couple of months."
Reid's last report, issued on 23 July, said there had yet to be definitive completion dates on two glazing packages.
Bovis Lend Lease, which is the construction manager on the project, refused to comment on the possibility of further delays.
It did issue a statement in June after it and other members of the project team, including QS Davis Langdon & Everest, were subject to attacks in the Scottish media.
The Bovis statement at the time said the issue of completion was up in the air. It said: "Until the building is finished there cannot be any absolute guarantees."