The details of what the investigators found is not known, but Mr Brown is taking legal advice after being handed a copy of the draft review on Friday to ensure it is factually accurate and provide feedback.
Crown Solicitor Simon Moore, QC, is providing legal advice to council chief executive Doug McKay, who commissioned the report.
A source said the parties were engaged in "highly confidential territory" that was legally privileged.
Yesterday afternoon, Mr McKay told the Herald the draft report was with Mr Brown for feedback. He said until the mayor's feedback had been received and given full consideration, he was unable to comment further. He would not comment on the issue of hotels rooms.
Mr McKay said the findings of the review would be made public.
The review's terms of reference relate to any use of council resources within the office of the mayor in respect of Mr Brown's relationship with Ms Chuang that contravene council policy, and any improper preferential treatment given to Ms Chuang as a council employee, contractor or adviser.
They also allow EY to probe "any other issues that the reviewers or chief executive considers relate to, or arise out of, the above matters".
Yesterday, Mr Brown's office refused to comment on the review, except to say the process was in Mr McKay's hands. His staff would not say who Mr Brown's legal adviser was and whether the mayor or ratepayers were picking up the tab.
The delay of the review, which was meant to take no longer than four weeks and stretched to seven weeks, is raising concerns among several right-leaning councillors.
First-termers Denise Krum and Linda Cooper said the review was affecting their ability to do their jobs. Said Ms Krum: "This is hanging over all our heads. It's the strangest seven weeks I can think of."
Councillor Cameron Brewer said the review needed to be released by Mr McKay immediately, saying the mayor had had more than enough time to ensure it was factually correct.
What happens next
* Len Brown provides feedback on the draft review. No timeframe for this.
* Mr Brown's feedback is considered and final report is prepared.
* Chief executive Doug McKay releases the report.