The Scottish Government has committed to an inquiry into the botched prosecutions, which has already led to more than £30 million in damages and legal fees, with that figure estimated to potentially rise to £100m.
Financial experts David Whitehouse and Paul Clark were arrested in 2014 after they were appointed administrators of the company that ran Rangers, which fell into administration in 2012.
The Crown has since said their prosecution was "malicious" and both men were awarded £10.5m each in damages.
Charles Green, who took over the club in June 2012, received £6.5m in damages after he and five others were charged with serious organised crime offences in relation to the acquisition of the club.
Legal action following these prosecutions is still ongoing, with the £400,000 contract with consulting giant Teneo for “litigation support” intended to help support the Lord Advocate.
Scottish Conservative MSP Russell Findlay said there remained a “concerning lack of transparency" around the scandal and its “ongoing fallout”.
He said: “It is remarkable to learn that the Scottish Government has handed £400,000 of taxpayers’ money to bankroll the Crown’s ongoing legal defence and without an open tendering process.
“There remains a concerning lack of transparency around the Crown‘s malicious prosecution scandal and its ongoing fallout.
“Tens of millions of pounds have already been lost to this debacle and every penny must be explained and accounted for. Public faith in the integrity of our justice system is paramount.”
On its website, Teneo states that it can help companies and governments “dramatically change the public’s understanding of a company’s role in high-stakes litigation” through a “well run communications strategy”.
The firm adds that it works with clients to have a “more complete understanding of how to manage the matter on an ongoing basis, as well as the implications for the company and its stakeholders”, as well as ensuring the result of legal action is “positioned accurately, in the context of significant scrutiny”.
A Scottish Government spokesperson said: “The contract is in respect of advice sought for ongoing cases relating to the prosecutions of certain individuals associated with Rangers FC.
" It is normal for Government to seek independent external expertise for important and complex cases. All costs will be subject to public finance and accountability rules.
“The position of the Scottish Government is clear in respect of the malicious prosecutions. In February 2021, the Scottish Parliament debated the subject of an inquiry into the prosecutions and voted in favour of a judge-led inquiry and the Scottish Government is committed to this course of action.
"As the First Minister explained on June 17, the exact form of inquiry will be determined once all legal proceedings in relation to the cases are concluded.”
Dorothy Bain, who replaced James Wolffe as Lord Advocate earlier this year after he stood down from the role, has recused herself from any matters relating to the litigation around the Rangers administration.