Fraser Wishart has resigned from his post as secretary of the Scottish Professional Footballers Association.
Wishart took over from Tony Higgins in December 2006
Wishart was promoted from assistant secretary to the union's senior officer following the departure of Tony Higgins in December 2006.
He said in a statement: "I have thoroughly enjoyed working full-time for the SPFA helping players.
"In the future, I aim to work in a capacity that will assist the development of the game in Scotland."
Former Motherwell, St Mirren, Falkirk, Rangers, Clydebank and Airdrieonians full-back Wishart retired from playing six years ago but had already been involved with the union as a committee member and president.
He became deputy assistant to Higgins, who quit the SPFA in December to take up a top post with world players' union Fifpro.
I will be in a position to consider and take up one of several new opportunities offered to me by people within the football industry
Wishart was involved in several high-profile cases over the last season.
He advised Andy Webster as the Scotland defender attempted to free himself of his contract at Hearts.
It led to claims that his use of a Fifa loophole to join Wigan Athletic would revolutionise the transfer system around Europe.
And Wishart helped advise Hearts players Steven Pressley, Paul Hartley and Craig Gordon, who were unhappy at the running of their club in October.
But Wishart was not available for interview following his resignation, with the reasons for his own departure unclear.
"After a short break with my family, I will be in a position to consider and take up one of several new opportunities offered to me by people within the football industry," he said in his statement.
Wishart has previous experience of coaching with Airdrie and Clydebank.