Keith Brown, who is now justice secretary, was doorstepped by journalists as he left the Holyrood chamber on Thursday.
However, he retreated into the Scottish Parliament’s canteen, insisting: "You've had a full response from the First Minister.
"I've nothing to add to the response from the First Minister."
It came after Scottish Conservative leader Douglas Ross accused the SNP of a cover-up over a key missing document.
There is ongoing controversy over a botched contract to build two ferries at the Ferguson shipyard in Port Glasgow.
The vessels, the Glen Sannox and the as-yet-unnamed hull 802, are at least £150 million over budget and five years late.
A recent report from Audit Scotland found there was “insufficient documentary evidence” to explain why the contract was given to the Ferguson shipyard, which has since been nationalised, without a full refund guarantee.
Speaking during First Minister’s Questions, Nicola Sturgeon said more than 200 documents relating to the decision had been put into the public domain.
But she conceded “there is one link in the chain that is missing”, saying: “There is one piece of documentation that is not there, which is the formal record of the decision to proceed with the final contract award.”
She said the decision to do so was “nevertheless clear in all of the surrounding documentation”.
Why ministers took this decision is still not known. Mr Brown, who was infrastructure secretary at the time, did not answer questions on the issue.
Tory MSP Stephen Kerr accused him of “cowering behind bangers and mash in the parliament canteen to avoid questions on the ferry scandal”.
Mr Brown later spoke to Channel 4 News, saying: "That document, the one that signed it off, if it ever existed, is not now available.”
He said disgraced former finance secretary Derek Mackay, who was then transport minister, approved the project and was in charge of safeguards.
Speaking in Holyrood, Ms Sturgeon said there was no evidence that the key document had been withheld, and Audit Scotland had made clear this was not its assessment.
Mr Ross called for any “gagging orders” on former Ferguson employees to be lifted, amid concerns over non-disclosure agreements.
The First Minister said: “Nobody – and let me say this very clearly – nobody in the employment of Ferguson shipyard will be prevented in any way, shape or form from speaking to Audit Scotland and speaking in full to Audit Scotland.”
Speaking after FMQs, Mr Ross said: “Four times in a row, Nicola Sturgeon couldn't answer where the most crucial document in the ferry fiasco has gone.
“When this ferries contract was awarded, Nicola Sturgeon said it was one of her proudest achievements.
"Now, we’re expected to believe there’s not a shred of evidence about why this decision was made or who made it.
“It's laughable. A few weeks ago the First Minister told us a big boy did it and ran away – now the dog’s eaten her homework.
"These excuses wouldn’t cut it in a primary school classroom.”
Richard Leonard, convener of Holyrood’s public audit committee, said it will now take evidence on the debacle from “relevant accountable officers who were in post when key decisions were made by the Scottish Government and Transport Scotland”.
The committee is widely expected to launch an inquiry in the coming weeks.