The solicitors said that Gary Withey, a partner at the firm, had parted company with them due to "family and personal reasons".
The lawyer – who advised Craig Whyte on his takeover of the club last year – has been embroiled in Rangers' administration process and had been accused of obstructing the investigation into the club's "missing millions".
Administrators Duff and Phelps said attempts to trace Mr Withey had "proved
extremely difficult". His resignation comes as the SPL launched an investigation into undisclosed payments to players and the administrators announced a further reprieve on potential job cuts at the club.
A spokesman for Collyer Bristow last night confirmed Mr Withey left the partnership and the firm on March 1.
The spokesman said: "We have been in contact with him and he is no longer a partner of the firm."
He added that the company was unaware of Mr Withey's whereabouts but had been in email contact with him for 10 days.
Mr Withey is accused of blocking access to a Collyer Bristow client account, believed to contain the rest of the £24.4 million Ticketus deal after £18m was used to pay off Lloyds Banking Group.
On Saturday, joint administrator David Whitehouse said: "We have been trying to speak to Gary Withey. It has proved difficult."
Problems at the club worsened yesterday as the SPL announced a probe into claims from former Rangers director Hugh Adam that some player payments were not included in official contracts.
A statement read: "The SPL board has instructed an investigation into the alleged non-disclosure to the SPL of payments by or on behalf of Rangers to players since July 1998."
SPL chief executive Neil Doncaster said: "First we have to establish whether there were any payments made that were undisclosed at the time and, if they were, we will take that forward."
Rangers' staff and players were still unclear on their future last night as administrators continued any decision on job cuts for a further day.