He becomes the fifth man to leave the SRU's executive board this week after the general committee moved to oust chairman David Mackay.
Non-executive directors Fraser Livingston, Andrew Flanagan and Eric Hagman quit on Tuesday in protest at Mackay's departure.
Mackay had received a no-confidence vote from the general committee, which fears a loss of its powers.
And a group of senior players were set to meet in Edinburgh on Tuesday night to discuss the developments.
"There is a lot of concern at the moment over the future and the lack of stability in the game and I felt it was important players got together to discuss their concerns," Glasgow winger Kenny Logan told the Scotsman.
"There is real concern over the removal of David Mackay, someone the players felt strongly was proving a good leader, and the decision of the other businessmen to quit Scottish rugby."
A joint-statement from Livingston, Flanagan and Hagman read: "Replacing the chairman without prior notice or any consultation whatsoever with the executive board flies in the face of good governance.
"In David Mackay's short term in charge of the board, enormous strides have been made in improving efficiency, planning debt reduction and developing a cohesive and comprehensive strategy for the game.
"Sadly, the general committee's actions do nothing to further the interests of taking Scottish rugby into the 21st century."
Fred McLeod, who was president in the 1996-97 season, was appointed interim chairman of Scottish Rugby with immediate effect after MacKay's resignation.
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Mackay, who could make a return under a new structure, was surprised by Monday's vote of no confidence and hoped that it would not halt what he viewed as an improvement in the fortunes of Scottish rugby.
"I am a fairly pragmatic person, but I would be an odd sort of character if I did not feel a degree of anger," he told BBC Sport.
"I am very strong in my view that we cannot have a strategic plan without proper governance.
"Some on the committee feel very differently from that, but they appoint the chairman and that's why I am no longer chairman.
"It is a business as well as a sport and any business needs a structure that can take rapid decisions. All other unions have it."
Mackay pointed out that a £19m loss in the financial year had been slashed to £1m in the present one.