The man at the centre of the Wendy Alexander illegal donation row has condemned "gross mismanagement" at the top of Scottish Labour.
Ms Alexander's leadership campaign team solicited a payment of £950 from Jersey-based businessman Paul Green.
Mr Green has told BBC Scotland his donation was clearly a personal cheque.
Speaking at Holyrood on Tuesday, Ms Alexander again refused to resign over the row and said she would continue to work to clear her name.
Ms Alexander, who is meeting her party's 45 other MSPs, claims she had not known that the cash broke electoral law.
The donation was illegal because it came from someone not on the electoral register.
She has rejected any suggestion of "intentional wrongdoing" and is expected to tell her colleagues that she would "tough out" the donations controversy.
Wendy Alexander will meet the party's other MSPs
Speaking to BBC Radio's Good Morning Scotland programme in his first interview since the row erupted, Mr Green said: "This has to be gross mismanagement.
"Looking at it from afar, who in their right mind is going to try and hide £950."
Mr Green said that when he was asked for the money for Ms Alexander's campaign by Labour MSP Charlie Gordon he sought and gained an assurance it was within donation guidelines.
He said there was "no doubt" his contribution was a personal cheque, accompanied by a personal letter from his home address in Jersey.
He said: "I am angry that I have been innocently embroiled in a national controversy, that's what's really upsetting me.
"When you have done nothing wrong, to find yourself banner headlines is not very pleasant."
Mr Green also gave £950 to the Labour Party in Glasgow South in April. Both donations were at the invitation of Mr Gordon.
Mr Green said Mr Gordon was an "honest and decent" man who must either have been misled or had not done his homework.
"I cannot see that there was any criminal intent," he said.
He added the Labour Party seemed to be "rather confused" and denied any suggestion that the donation had been "payback" for business connections in Glasgow down the years.
"I hardly think so," he replied. "What does £950 buy you these days?"
He said it was "a pretty safe bet" that he would not be making any further donations to the party.
If the cheques are returned he plans to donate the cash to Children in Need, adding: "Hopefully that donation will not be quite as controversial."
Speaking at Holyrood on Tuesday, Mr Gordon told journalists that he still strongly supported Ms Alexander.
However, he would not comment on Mr Green's statement.
Mr Gordon added that he would make an announcement about his political future later in the week.
Ms Alexander is understood to be confident that the Electoral Commission inquiry will find that she did not deliberately breach the law on donations to political parties.
Charlie Gordon has resigned as Labour transport spokesman
But the SNP have insisted that she is under orders from London to stay on as Scottish leader to act as a "human shield" for Prime Minister Gordon Brown and Labour's Deputy Leader Harriet Harman, who are both caught up in a separate donations row at Westminster.
The regular Tuesday meeting of the Labour group at Holyrood will have to decide whether to support Ms Alexander's "tough it out" policy.
Meanwhile, the hunt is on for the "mole" who leaked the names of donors to the Sunday Herald newspaper.
Two Labour peers, Lord Maxton and Baroness Adams, have asked the police to investigate.
They said that because they donated less than £1,000, they should have been able to remain anonymous under electoral law.