Mr Nager took his concerns about ACC and his employer's actions to the Northern Advocate, which published a story on March 15. On Monday morning Mr Nager was informed his employment had been terminated as of March 19.
He has already lodged a complaint with the Privacy Commissioner and is in the process of taking a case for unjustified dismissal, among other things, to the Employment Relations Authority.
Regional council chief executive Malcolm Nicolson said he could not comment on staff-related issues.
ACC has confirmed the original report was incorrect and has also sought its return from the council.
However, an ACC spokeswoman said it did not contain information that would not normally be shared with an employer.
That is disputed by ACC advocate Alex Taylor, who said he could not imagine a worse privacy breach.
The report, which detailed medications and the psychological effects of the attack, had "hopelessly compromised" Mr Nager's ability to go back to his job or even find other work in the same field, Mr Taylor said.
It was not the first time medical information had been wrongly released to an employer but it was the worst case he knew of.
Mr Taylor, who is handling Mr Nager's case, said it was unusual for an employer to refuse to destroy information released in error, but ACC had put the council in an awkward position. No employer should have to grapple with ethics of acting on information it was not supposed to have, he said.
Mr Taylor said he had seen evidence that the council's stance on Mr Nager's employment had changed after receiving the report.
The Office of the Privacy Commissioner does not comment on specific cases. Its advice for anyone who finds private information, or receives it in error, is to return it to the agency it came from.