Gary Withey suddenly resigned from Collyer Bristow, which represented Whyte, shortly after administrators were called into the club in February.
The London-based firm is now facing a claim of professional negligence over the deal, in which Whyte bought the club for £1 last May.
Originally Mr Withey had cited family reasons for his departure, but last night he admitted he had been unable to face his partners as the controversy intensified.
He told The Herald: "I was most embarrassed and ashamed that such a high-profile case would fall on a law firm that had been in existence for almost 270 years.
"Comments were being made in the press that were not true about failing to co-operate and the firm was receiving a number of calls and emails from very irate – understandably irate – fans. I couldn't look my partners in the eyes.
"It is a good law firm and it doesn't deserve the opprobrium being poured on it. I wanted to do the right thing and I felt very strongly about that."
Mr Withey said he could not comment on the negligence claim that is being prepared by administrators Duff & Phelps against Collyer Bristow, which the legal firm earlier said it would "vigorously defend".
"I don't know anything about it," Mr Withey claimed.
The lawyer, who has more than 20 years' experience, said he was unsure what his professional future would hold given that the Rangers case continues to be a "black cloud" hanging over those involved.
Mr Withey has now been hired by Segens Blount Petre Solicitors in London, which specialises in business affairs, civil cases and commercial litigation.
When asked what impact the Rangers crisis had had on him, Mr Withey said: "It will continue to affect everything while there is a view that I personally benefited from the Rangers deal. The reality is that I didn't personally benefit in any way, not to the tune of a single penny.
"Indeed, you will see that my old firm didn't benefit either. They are owed £40,000 by Rangers, as you will see from the list of creditors.
"In addition, everything the firm did for Rangers was done at a heavily discounted price of around 30-35% to bring us down to about the same as Scottish law firms would charge. We didn't want Rangers to pay any more than they would pay in Scotland.
"This was at my insistence. It is unusual but that is how we treated them. They were a special client and we gave them a special discount."
Mr Withey, who was named as Rangers secretary following Whyte's takeover, said he last saw Whyte at a private members' club in London three weeks ago. He described the meeting as "civil, nothing more, nothing less" but yesterday admitted he regretted the day he was instructed by the multi-millionaire.
He added: "I didn't have a single concern about him, which worries me. There were a number of good recommendations – he was wealthy, he was a good businessman and he did a lot of deals. I was told he had significant money behind him.
"I had a fairly steady legal career for 21 years and it seems I managed to get instructed by a client who I now realise doesn't seem to have any feeling or thought for anyone he got involved in. Everything to him was collateral damage."
Mr Withey described Whyte as secretive and said he began to have doubts about him during dealings with Her Majesty's Revenue and Customs (HMRC).
"The HMRC were incredibly aggressive towards him and the club and I could never work out why," he added.
"It was as though people knew there was something that I didn't. I couldn't make sense why they were so aggressive and Whyte is a very secretive person."
Duff & Phelps is due to return to the High Court in London on Monday to present their claim against Collyer Bristow.
The hearing follows the administrators' successful attempt to secure more than £3.6 million from Whyte's client account held there, which Duff & Phelps said was owed to Rangers.
All parties were due to return to court last month on this matter, but proceedings were suspended after Duff & Phelps announced it had "substantially wider claims" to bring against the London-based law firm.