The Scotsman reports that Donnie will announce his retirement today.
Donnie is just 28, but the openside flanker has endured a horrendous run of bad luck with injuries over the past four years and started only 11 games in the past three seasons, including two this year.
A hugely popular figure among the pro ranks, he has also watched and helped guide the next generation of back row talent, particularly John Barclay, through to pro and international level.
A young player of the year and Scotland Under-21 captain, Macfadyen made his Scotland debut against Canada in 2002 and went on to win 11 caps, playing against Australia four times, outshining George Smith and Phil Waugh, and South Africa on three occasions, scoring in his last match against them in 2006.
However, a succession of injuries, the latest being a knee problem and subsequent infection suffered last summer, has caused numerous problems for his body and demoralising set-backs mentally, even for a player with his incredibly positive approach to life. In the past few weeks, he has also had to cope with the loss of his father, the well-respected judge Lord Macfadyen, to cancer.
Donnie told glasgowwarriors.org: I take with me some fantastic memories of playing for Glasgow. Injuries have played such a big part in my career, but all the good times by far outweigh the bad.
Having played such a big part in the development of future back-row talent, such as John Barclay, Donnie is pleased to see the Warriors go from strength-to-strength in his department. Its great to see such talented young guys come through. Glasgow have really set themselves up for a good run next year and I look forward to seeing both Scottish professional teams flourishing in the years ahead.